# Brittonic languages

The Brittonic languages (also Brythonic or British Celtic; Welsh: ieithoedd Brythonaidd/Prydeinig; Cornish: yethow brythonek/predennek; and Breton: yezhoù predenek) form one of the two branches of the Insular Celtic languages; the other is Goidelic. It comprises the extant languages Breton, Cornish, and Welsh. The name Brythonic was derived by Welsh Celticist John Rhys from the Welsh word Brython, meaning Ancient Britons as opposed to an Anglo-Saxon or Gael.
The Brittonic languages derive from the Common Brittonic language, spoken throughout Great Britain during the Iron Age and Roman period. In the 5th and 6th centuries emigrating Britons also took Brittonic speech to the continent, most significantly in Brittany and Britonia. During the next few centuries, in much of Britain the language was replaced by Old English and Scottish Gaelic, with the remaining Common Brittonic language splitting into regional dialects, eventually evolving into Welsh, Cornish, Breton, Cumbric, and probably Pictish. Welsh and Breton continue to be spoken as native languages, while a revival in Cornish has led to an increase in speakers of that language. Cumbric and Pictish are extinct, having been replaced by Goidelic and Anglic speech. The Isle of Man and Orkney may also have originally spoken a Brittonic language, but this was later supplanted by Goidelic on the Isle of Man and Norse on Orkney. There is also a community of Brittonic language speakers in Y Wladfa (the Welsh settlement in Patagonia).

## Name

The names "Brittonic" and "Brythonic" are scholarly conventions referring to the Celtic languages of Britain and to the ancestral language they originated from, designated Common Brittonic, in contrast to the Goidelic languages originating in Ireland. Both were created in the 19th century to avoid the ambiguity of earlier terms such as "British" and "Cymric". "Brythonic" was coined in 1879 by the Celticist John Rhys from the Welsh word Brython. "Brittonic", derived from "Briton" and also earlier spelled "Britonic" and "Britonnic", emerged later in the 19th century. "Brittonic" became more prominent through the 20th century, and was used in Kenneth H. Jackson's highly influential 1953 work on the topic, Language and History in Early Britain. Jackson noted by that time that "Brythonic" had become a dated term: "of late there has been an increasing tendency to use Brittonic instead." Today, "Brittonic" often replaces "Brythonic" in the literature. Rudolf Thurneysen used "Britannic" in his influential A Grammar of Old Irish, although this never became popular among subsequent scholars.
Comparable historical terms include the Medieval Latin lingua Britannica and sermo Britannicus and the Welsh Brythoneg. Some writers use "British" for the language and its descendants, although, due to the risk of confusion, others avoid it or use it only in a restricted sense. Jackson, and later John T. Koch, use "British" only for the early phase of the Common Brittonic language.
Before Jackson's work, "Brittonic" and "Brythonic" were often used for all the P-Celtic languages, including not just the varieties in Britain but those Continental Celtic languages that similarly experienced the evolution of the Proto-Celtic language element /kʷ/ to /p/. However, subsequent writers have tended to follow Jackson's scheme, rendering this use obsolete.
The name "Britain" itself comes from Latin: Britannia~Brittania, via Old French Bretaigne and Middle English Breteyne, possibly influenced by Old English Bryten[lond], probably also from Latin Brittania, ultimately an adaptation of the native word for the island, *Pritanī.
An early written reference to the British Isles may derive from the works of the Greek explorer Pytheas of Massalia; later Greek writers such as Diodorus of Sicily and Strabo who quote Pytheas' use of variants such as πρεττανική (Prettanikē), "The Britannic [land, island]", and νησοι βρεττανιαι (nēsoi brettaniai), "Britannic islands", with Pretani being a Celtic word that might mean 'painted ones' or 'tattooed folk', referring to body decoration.

## Evidence

Knowledge of the Brittonic languages comes from a variety of sources. The early language's information is obtained from coins, inscriptions, and comments by classical writers as well as place names and personal names recorded by them. For later languages, there is information from medieval writers and modern native speakers, together with place names. The names recorded in the Roman period are given in Rivet and Smith.

## Characteristics

The Brittonic branch is also referred to as P-Celtic because linguistic reconstruction of the Brittonic reflex of the Proto-Indo-European phoneme *kʷ is p as opposed to Goidelic k. Such nomenclature usually implies acceptance of the P-Celtic and Q-Celtic hypothesis rather than the Insular Celtic hypothesis because the term includes certain Continental Celtic languages as well. Other major characteristics include:
* The retention of the Proto-Celtic sequences *am and *an, which mostly result from the Proto-Indo-European syllabic nasals.
* Celtic /w/ (written u in Latin texts and ou in Greek) became gw- in initial position, -w- internally, whereas in Gaelic it is f- in initial position and disappears internally:
** Proto-Celtic *windos 'white, fair' became Welsh gwyn (masculine), gwen (feminine), Cornish gwynn, Breton gwenn. Contrast Irish fionn 'fair'.
** Proto-Celtic *wassos 'servant, young man' became Welsh, Cornish, and Breton gwas. Contrast Middle Irish foss.
Initial s-:
* Initial s- followed by a vowel was changed to h-:
** Welsh hen 'old', hir 'long', hafal 'similar'
** Cornish hen 'ancient', hir 'long', haval 'similar'
** Breton hen 'ancient', hir 'long', hañval 'similar'
** Contrast Irish sean 'old', síor 'long', samhail 'similarity'
* Initial s- was lost before /l/, /m/ and /n/:
** *slemon became Welsh llyfn, Cornish leven and Breton levn 'smooth'. Contrast Irish sleamhain 'smooth, slimy'
** *smeru became Welsh mêr, Cornish mer, and Breton mel 'marrow'. Contrast Irish sméar
* The initial clusters sp-, sr-, sw- became f-, fr-, chw-:
** *sɸera became Welsh ffêr 'ankle', Cornish fer 'shank, lower leg' and Breton fer 'ankle'. Contrast Old Irish seir 'heel, ankle'
** *srogna 'nostril' became Welsh ffroen, Cornish frig and Breton froen. Contrast Irish srón
** *swīs 'you' (plural) became Welsh chwi, Cornish hwi and Breton c'hwi. Contrast Old Irish síi
Lenition:
* Voiceless plosives become voiced plosives in intervocalic position.
** d [d], g [ɡ], b [b]
** Contrast Irish th, ch, ph
* Voiced plosives /d/, /ɡ/ (later /ɣ/ or /j/, then lost in Welsh and Cornish; remained as /ɣ/ in Breton), /b/, and /m/ became soft spirants in an intervocalic position and before liquids:
** Welsh dd [ð], f [v]
** Cornish dh [ð], v [v]
** Breton z [z], c'h [ɣ], v [v]
** Contrast Irish dh, gh, bh, mh
Voiceless spirants:
* Geminated voiceless plosives transformed into spirants; /pp/ (pp), /kk/ (cc), /tt/ (tt) became /ɸ/ (later /f/), /x/ (ch/c'h), /θ/ (th/zh) before a vowel or liquid:
** *cippus > Breton kef, Cornish kyf, Welsh cyff, 'tree trunk'
** *cattos > Breton kazh, Cornish kath, Welsh cath, 'cat' vs. Irish cat
** *bucca > Breton boc'h, Cornish bogh, Welsh boch, 'cheek'
* Voiceless stops become spirants after liquids:
** *artos 'bear' > Welsh/Cornish arth, Breton arzh, compare Old Irish art
Nasal assimilation:
* Voiced stops were assimilated to a preceding nasal:
* Brittonic retains original nasals before -t and -k, whereas Goidelic alters -nt to -d, and -nk to -g:
** Breton kant 'hundred' vs. Irish céad; Breton Ankou '[personification of] Death', Irish éag 'die'

## Classification

The family tree of the Brittonic languages is as follows:
* Common Brittonic
** Western Brittonic
*** Cumbric
*** Welsh
** Southwestern Brittonic
*** Cornish
*** Breton
Brittonic languages in use today are Welsh, Cornish and Breton. Welsh and Breton have been spoken continuously since they formed. For all practical purposes Cornish died out during the 18th or 19th century, but a revival movement has more recently created small numbers of new speakers. Also notable are the extinct language Cumbric, and possibly the extinct Pictish. One view, advanced in the 1950s and based on apparently unintelligible ogham inscriptions, was that the Picts may have also used a non-Indo-European language. This view, while attracting broad popular appeal, has virtually no following in contemporary linguistic scholarship.

## History and origins

The modern Brittonic languages are generally considered to all derive from a common ancestral language termed Brittonic, British, Common Brittonic, Old Brittonic or Proto-Brittonic, which is thought to have developed from Proto-Celtic or early Insular Celtic by the 6th century BC.
A major archaeogenetics study uncovered a migration into southern Britain in the middle to late Bronze Age, during the 500-year period 1,300–800 BC. The newcomers were genetically most similar to ancient individuals from Gaul. During 1,000–875 BC, their genetic markers swiftly spread through southern Britain, but not northern Britain. The authors describe this as a "plausible vector for the spread of early Celtic languages into Britain". There was much less inward migration during the Iron Age, so it is likely that Celtic reached Britain before then. Barry Cunliffe suggests that a Goidelic branch of Celtic may already have been spoken in Britain, but that this middle Bronze Age migration would have introduced the Brittonic branch.
Brittonic languages were probably spoken before the Roman invasion throughout most of Great Britain, though the Isle of Man later had a Goidelic language, Manx. During the period of the Roman occupation of what is now England and Wales (AD 43 to c. 410), Common Brittonic borrowed a large stock of Latin words, both for concepts unfamiliar in the pre-urban society of Celtic Britain such as urbanization and new tactics of warfare, as well as for rather more mundane words which displaced native terms (most notably, the word for 'fish' in all the Brittonic languages derives from the Latin piscis rather than the native *ēskos – which may survive, however, in the Welsh name of the River Usk, Wysg). Approximately 800 of these Latin loan-words have survived in the three modern Brittonic languages. Pictish may have resisted Latin influence to a greater extent than the other Brittonic languages.
It is probable that at the start of the Post-Roman period, Common Brittonic was differentiated into at least two major dialect groups – Southwestern and Western. (Additional dialects have also been posited, but have left little or no evidence, such as an Eastern Brittonic spoken in what is now the East of England.) Between the end of the Roman occupation and the mid-6th century, the two dialects began to diverge into recognizably separate varieties, the Western into Cumbric and Welsh, and the Southwestern into Cornish and its closely related sister language Breton, which was carried to continental Armorica. Jackson showed that a few of the dialect distinctions between West and Southwest Brittonic go back a long way. New divergencies began around AD 500 but other changes that were shared occurred in the 6th century. Other common changes occurred in the 7th century onward and are possibly due to inherent tendencies. Thus the concept of a Common Brittonic language ends by AD 600. Substantial numbers of Britons certainly remained in the expanding area controlled by Anglo-Saxons, but over the fifth and sixth centuries they mostly adopted the Old English language and culture.

### Decline

The Brittonic languages spoken in what are now Scotland, the Isle of Man, and England began to be displaced in the 5th century through the settlement of Irish-speaking Gaels and Germanic peoples. Henry of Huntingdon wrote c. 1129 that Pictish was "no longer spoken".
The displacement of the languages of Brittonic descent was probably complete in all of Britain except Cornwall, Wales, and the English counties bordering these areas such as Devon, by the 11th century. Western Herefordshire continued to speak Welsh until the late nineteenth century, and isolated pockets of Shropshire speak Welsh today.

### Sound changes

The large array of Brittonic sound changes has been documented by Schrijver (1995), building upon Jackson (1953).

#### Changes to long vowels and diphthongs

Brittonic has undergone an extensive remodeling of Proto-Celtic diphthongs and long vowels. All original Proto-Celtic diphthongs turned into monophthongs, albeit a number of these re-diphthongized at later stages.
Brittonic default outcomes of long vowels and diphthongs :
| Proto-Celtic | Proto-Brythonic | Welsh | Cornish | Breton |
| *ū | *i | i | i | i |
| *ē | *i | i | i | i |
| *ī | *i | i | i | i |
| *eu | *ọ̄>ʉ | u | u, uy | u |
| *ou | *ọ̄>ʉ | u | u/uy | u |
| *oi | *ọ̄>ʉ | u | u/uy | u |
| *ei | *ẹ̄>uɨ | wy | o/oy | oe/oue/oa |
| *ai | *oɨ | oe | o/oy | oa |
| *ā | *ọ | aw/o | ue,u | eu/e |
| *au | *ọ | aw/o | ue,u | eu/e |

#### Changes to short vowels

The distribution of Proto-Celtic short vowels were reshuffled by various processes in Brittonic, such as the two i-affections, a-affection, raisings, and contact with lenited consonants like *g > /ɣ/ and *s > *h.
The default outcomes of stressed short vowels in Brittonic are as follows:
Brittonic default outcomes of stressed short vowels :
| Proto-Celtic short vowel | Welsh | Cornish | Breton |
| *a | a | a | a |
| *e | e | e | e |
| *i | ɨ ⟨y⟩ | ɪ ⟨y, e⟩ (Old Cornish) e (later) | ɪ ⟨i, e⟩ (Old Breton) e (later) |
| *o | o | o | o |
| *u | u ⟨w⟩ | o | o(u) |

##### Raisings of *e and *o

Welsh exhibits raisings of *e to *i > *ɪ > ɨ ⟨y⟩ and *o > /u/ ⟨w⟩ before a nasal followed by a stop.
It is difficult to determine whether the raising from *o to *u also affected Cornish and Breton, since both of those languages generally merge *o with *u.
The raising of *e to *i occurred in all three major Brittonic languages:
* Proto-Celtic *sentus "path" > *hɪnt > Middle Welsh hynt, Middle Cornish hyns, and Old Breton scoiu-hint "side-passage".
Other raising environments identified by Schrijver include:
* When the vowel is preceded by *m and followed by *n.
* When the vowel is in a pretonic syllable, preceded by an alveolar consonant and followed by a nasal.
* When the vowel is followed by an *r which in turn is followed by either *n or a velar consonant.
This raising preceded a-affection, since a-affection reverses this raising whenever it applied.
All these raisings not only affected native vocabulary, but also affected Latin loanwords.
Raising of *e and *o, examples derived from Schrijver (1995) :
| Proto-form | Late Proto-Brittonic | Welsh | Cornish | Breton |
| Raising before a nasal followed by a stop |||||
| *kentus "first, early" | *kɪnt | cynt | kens | kent |
| *kʷenkʷe "five" | *pɪmp | pymp | pemp | pemp |
| *sondos "this" | *hunn | hwn(n) | N/A | N/A |
| Raising in *mVn- sequences |||||
| *menmens "mind" | *mɪnw | mynw | N/A | meno |
| *moniklos "neck" | *munugl | mwnwgl | N/A | N/A |
| Raising between alveolar and nasal consonants in pretonic syllables |||||
| *Demet- (tribal name) | *Dɪβ̃ed | Dyfed | N/A | N/A |
| *nemetos "venerated" | *nɪβ̃ed | -nivet (Old Welsh) -nyfet (Middle Welsh) | N/A | -nimet, -nemet (Old Breton) |
| *temes(e)los "dark(ness)" | *tɪβ̃uɪl | tywyll | N/A | timuil (Old Breton) teñval (modern Breton) |
| Latin sonus "sound" | *son (sg.) *sunow (pl.) | son, swn | son | so(u)n |
| Raising in *Vrn and *VrK sequences |||||
| *ast-kornu "bone" | *askurn | asgwrn | ascorn | asko(u)rn |
| *tigernos "lord" | *tɪɣɪrn | teyrn | mech-deyrn | mach-tiern (Old Breton) |
| *borg- "throw" | *burɣ | bwrw | N/A | N/A |
| *org- "to strike down" | *urɣ | dygyfwrw (prefixed with to-kom-) | N/A | N/A |
| *yorkos "roebuck" | *jurx | iwrch | yorch (Old Cornish) | yourc'h |

##### Interactions of vowels followed by *g

Multiple special interactions of vowels occurred when followed by *g.
* *e in such environments can be raised to *ɪ or lowered to *a depending on the following sound.
* *ig > *ɪɣ had a special Welsh development in which it would become e in any environment where internal i-affection would apply. This development affected not only *ig > *ɪɣ, but also *eg > *ɪɣ.
* The -a- in Welsh Cymraeg "Welsh language" and Cymraes "Welshwoman" (both from a base *kom-mrog-) has been explained from a special development of *-og- to *-ag- pre-apocope antepenultimate syllables.
Outcomes of vowels before *g in Brittonic :
| Proto-form | Late Proto-Brittonic | Welsh | Cornish | Breton |
| *ege, *egi > *age, *agi |||||
| *segetlā "plough-handle" | *haɣeðl | haeddel | N/A | hae(z)l |
| *dregenom "blackthorn" | *draɣen | draen | N/A | draen |
| *egV > *ɪgV if not lowered to *ag |||||
| *tegos "house" | *tɪɣ | tŷ | chy | ti |
| *segos "bold, brave" | *hɪɣ | hy | N/A | N/A |
| *ig- > *ɪɣ > *e in Welsh in internal i-affection environments |||||
| *tigernos "lord" | *tɪɣɪrn | teyrn | mech-deyrn | mach-tiern (Old Breton) |
| *brigantī "privilege" | *brɪɣẹnt | bryeint (Old Welsh) breint (Middle Welsh) braint (Modern Welsh) | N/A | Brient (Old Breton) |
| *wegatikos "woven" | *gwɪɣẹdɪg | gweedig | N/A | N/A |
| Latin Segontium) | *sɪɣönt | Segeint (Old Welsh) Seint (Middle Welsh) | N/A | N/A |

##### Assimilation of *oRa to *aRa

Closely paralleling the common Celtic change of *eRa > *aRa (Joseph's rule) is the change of *oRa to *aRa in Brittonic, with R standing for any lone sonorant. Unlike Joseph's rule, *oRa to *aRa did not occur in Goidelic. Schrijver demonstrates this rule with the following examples:
* Proto-Celtic *kolanV- "corpse": Welsh celain, plural calanedd vs. Irish colainn
* Proto-Celtic *toranos "thunder": taran in all three Brittonic languages vs. Irish torann
Assuming that Welsh manach (borrowed from Latin monachus "monk") also underwent this assimilation, Schrijver concludes that this change must predate the raising of vowels in *mVn- sequences, which in turn predates a-affection (an early fifth-century process).

##### /je/ > /ja/

In Brittonic, Celtic *ye generally became /ja/. Some examples cited by Schrijver include:
* Proto-Celtic *yegis > Brittonic *jaɣ > Welsh iâ "ice" vs. Old Irish aig, genitive ega (the a in the Irish word arose via an unrelated development involving *g)
* Proto-Celtic *yestu "boiling" > Brittonic *jas > Welsh ias vs. early Irish ess "cataract"
* Proto-Celtic *gyemos "winter" > Brittonic *gəijaβ̃ > Welsh gaeaf vs. Irish gaim, gem (-a- analogical)

##### *wo

The sequence *wo was quite volatile in Brittonic. It originally manifested as *wo in unlenited position and *wa in lenited position. Word-initially, this allomorphy was gone in medieval times, leveled out in various ways. Whichever of *o or *a to be generalized in the reflexes of a word in a given Brittonic language is completely unpredictable, and occasionally both o and a reflexes have been attested within the same language. Southwest Brittonic languages like Breton and Cornish usually generalize the same variant of *wo in a given word while Welsh tends to have its own distribution of variants.
The distribution of *wo/wa is also complicated by an Old Breton development where *wo that had not turned to *gwa would split into go(u)- (Old Breton gu-) in penultimate post-apocope syllables and go- in monosyllables.

##### Developments of *ub

The sequence *ub > *uβ remained as such when followed by a consonant, for instance in Proto-Celtic *dubros "water" > *duβr > Welsh dwfr, dŵr and Breton dour.
However, if no consonant exists after a *ub sequence, the *u merges with whatever Proto-Celtic *ou and *oi became, the result of which is written ⟨u⟩ in the Brittonic languages. The lenited *b > *β is lost word-finally after this happens.
* *dubus "black" > Welsh du, Cornish du, Breton du
* *lubV- "herb" > Old Breton tutlub, tutlob > Breton tule, tulo
* Latin cubitus > Middle Welsh kufyt, modern Welsh cufydd
Schrijver dates this development between the 6th to 8th centuries, with subsequent loss of *β datable to the 9th century.

##### a-affection

In Brittonic, final a-affection was triggered by final-syllable *ā or *a, which was later apocopated. This process lowered *i and *u in the preceding syllable to *e and *o, respectively.
A-affection, by affecting feminine forms of adjectives and not their masculine counterparts, created root vowel alternations by gender such as *windos, feminine *windā > *gwɪnn, feminine *gwenn > Welsh gwyn, feminine gwen.

##### i-affection

There were two separate processes of i-affection in Brittonic: final i-affection and internal i-affection. Both processes caused the fronting of vowels.

#### Simplified summary of consonantal outcomes

The regular consonantal sound changes from Proto-Celtic to Welsh, Cornish, and Breton are summarised in the following table. Where the graphemes have a different value from the corresponding IPA symbols, the IPA equivalent is indicated between slashes. V represents a vowel; C represents a consonant.
| Proto-Celtic | Late Brittonic | Welsh | Cornish | Breton |
| *b- | *b- | b | b | b |
| *-bb- | *-b- | b | b | b |
| *-VbV- | *-VβV- > -VvV- | f /v/ | v | v |
| *d- | *d- | d | d | d |
| *-dd- | *-d- | d | d | d |
| *-VdV- | *-VðV- | dd /ð/ | dh /ð/ | z /z/ or lost |
| *g- | *g- | g | g | g |
| *-gg- | *-g- | g | g | g |
| *-VgV- | *-VɣV- > -VjV- | (lost) | (lost) | (lost) |
| *ɸ- | (lost) | (lost) | (lost) | (lost) |
| *-ɸ- | (lost) | (lost) | (lost) | (lost) |
| *-xt- | *-xθ- > -(i)θ | th /θ/ | th /θ/ | zh /z/ or /h/ |
| *j- | *i- | i | i | i |
| *-j | *-ð | -dd /ð/ | -dh /ð/ | -z /z/ or lost |
| *k- | *k- | c /k/ | k | k |
| *-kk- | *-x- | ch /x/ | gh /h/ | c'h /x/ or /h/ |
| *-VkV- | *-g- | g | g | g |
| *kʷ- | *p- | p | p | p |
| *-kʷ- | *-b- | b | b | b |
| *l- | *l- | ll /ɬ/ | l | l |
| *-ll- | *-l- | l | l | l |
| *-VlV- | *-l- | l | l | l |
| *m- | *m- | m | m | m |
| *-mb- | *-mm- | m | m | m |
| *-Cm- | *-m- | m | m | m |
| *-m- | *-β̃- | f /v/, w | v | ñv /-̃v/ |
| *n- | *n- | n | n | n |
| *-n- | *-n- | n | n | n |
| *-nd- | *-nn- | n, nn | n, nn | n, nn |
| *-nt- | *-nt- | nt, nh /n̥/ | nt | nt |
| *-pp- | *-ɸ- > -f- | ff /f/ | f | f |
| *r- | *r- | rh /r̥/ | r | r |
| *sr- | *fr- | ffr /fr/ | fr | fr |
| *-r- | *-r- | r | r | r |
| *s- | *h-, s | h, s | h, s | h or lost, s |
| *-s- | *-s- | s | s | s |
| *sl- | *l- | ll /ɬ/ | l | l |
| *sm- | *m- | m | m | m |
| *sn- | *n- | n | n | n |
| *sɸ- | *f- | ff /f/ | f | f |
| *sw- | *hw- | chw /xw/ | hw /ʍ/ | c'ho /xw/ |
| *t | *t | t | t | t |
| *-t- | *-d- | d | d | d |
| *-tt- | *-θ- | th /θ/ | th /θ/ | zh /z/ or /h/ |
| *w- | *ˠw- > ɣw- > gw- | gw | gw | gw |
| *-VwV- | *-w- | w | w | w |
| *-V | *-Vh | Vch /Vx/ | Vgh /Vh/ | Vc'h /Vx/ or /Vh/ |

## Remnants in England, Scotland and Ireland
### Place names and river names

The principal legacy left behind in those territories from which the Brittonic languages were displaced is that of toponyms (place names) and hydronyms (names of rivers and other bodies of water). There are many Brittonic place names in lowland Scotland and in the parts of England where it is agreed that substantial Brittonic speakers remained (Brittonic names, apart from those of the former Romano-British towns, are scarce over most of England). Names derived (sometimes indirectly) from Brittonic include London, Penicuik, Perth, Aberdeen, York, Dorchester, Dover, and Colchester. Brittonic elements found in England include bre- and bal- for 'hill', while some such as co[o]mb[e] (from cwm) for 'small deep valley' and tor for 'hill, rocky headland' are examples of Brittonic words that were borrowed into English. Others reflect the presence of Britons such as Dumbarton – from the Scottish Gaelic Dùn Breatainn meaning 'Fort of the Britons', and Walton meaning (in Anglo-Saxon) a tun 'settlement' where the Wealh 'Britons' still lived.
The number of Celtic river names in England generally increases from east to west, a map showing these being given by Jackson. These include Avon, Chew, Frome, Axe, Brue and Exe, but also river names containing the elements der-/dar-/dur- and -went e.g. Derwent, Darwen, Deer, Adur, Dour, Darent, and Went. These names exhibit multiple different Celtic roots. One is *dubri- 'water' (Breton dour, Cumbric dowr, Welsh dŵr), also found in the place-name Dover (attested in the Roman period as Dubrīs); this is the source of rivers named Dour. Another is deru̯o- 'oak' or 'true' (Bret. derv, Cumb. derow, W. derw), coupled with two agent suffixes, -ent and -iū; this is the origin of Derwent, Darent, and Darwen (attested in the Roman period as Deru̯entiō). The final root to be examined is went/uent. In Roman Britain, there were three tribal capitals named U̯entā (modern Winchester, Caerwent, and Caistor St Edmunds), whose meaning was 'place, town'.

### Brittonicisms in English

Some, including J. R. R. Tolkien, have argued that Celtic has acted as a substrate to English for both the lexicon and syntax. It is generally accepted that Brittonic effects on English are lexically few, aside from toponyms, consisting of a small number of domestic and geographical words, which "may" include bin, brock, carr, comb, crag and tor. Another legacy may be the sheep-counting system yan tan tethera in the north, in the traditionally Celtic areas of England such as Cumbria. Several words of Cornish origin are still in use in English as mining-related terms, including costean, gunnies, and vug.
Those who argue against the theory of a more significant Brittonic influence than is widely accepted point out that many toponyms have no semantic continuation from the Brittonic language. A notable example is Avon which comes from the Celtic term for river abona or the Welsh term for river, afon, but was used by the English as a personal name. Likewise the River Ouse, Yorkshire, contains the Celtic word usa which merely means 'water' and the name of the river Trent simply comes from the Welsh word for a 'trespasser' (figuratively suggesting 'overflowing river').
Scholars supporting a Brittonic substrate in English argue that the use of periphrastic constructions (using auxiliary verbs such as do and be in the continuous/progressive) of the English verb, which is more widespread than in the other Germanic languages, is traceable to Brittonic influence. Others, however, find this unlikely since many of these forms are only attested in the later Middle English period; these scholars claim a native English development rather than Celtic influence. Ian G. Roberts postulates Northern Germanic influence, despite such constructions not existing in Norse. Literary Welsh has the simple present Caraf = 'I love' and the present stative (al. continuous/progressive) Yr wyf yn caru = 'I am loving', where the Brittonic syntax is partly mirrored in English. (However, English I am loving comes from older I am a-loving, from still older ich am on luvende 'I am in the process of loving'). In the Germanic sister languages of English, there is only one form, for example Ich liebe in German, though in colloquial usage in some German dialects, a progressive aspect form has evolved which is formally similar to those found in Celtic languages, and somewhat less similar to the Modern English form, e.g. 'I am working' is Ich bin am Arbeiten, literally: 'I am on the working'. The same structure is also found in modern Dutch (Ik ben aan het werk), alongside other structures (e.g. Ik zit te werken, lit. 'I sit to working'). These parallel developments suggest that the English progressive is not necessarily due to Celtic influence; moreover, the native English development of the structure can be traced over 1000 years and more of English literature.
Some researchers (Filppula, et al., 2001) argue that other elements of English syntax reflect Brittonic influences. For instance, in English tag questions, the form of the tag depends on the verb form in the main statement (aren't I?, isn't he?, won't we?, etc.). The German nicht wahr? and the French n'est-ce pas?, by contrast, are fixed forms which can be used with almost any main statement. It has been claimed that the English system has been borrowed from Brittonic, since Welsh tag questions vary in almost exactly the same way.

### Brittonic effect on the Goidelic languages

Far more notable, but less well known, are Brittonic influences on Scottish Gaelic, though Scottish and Irish Gaelic, with their wider range of preposition-based periphrastic constructions, suggest that such constructions descend from their common Celtic heritage. Scottish Gaelic contains several P-Celtic loanwords, but, as there is a far greater overlap in terms of Celtic vocabulary than with English, it is not always possible to disentangle P- and Q-Celtic words. However, some common words such as monadh = Welsh mynydd, Cumbric monidh are particularly evident.
The Brittonic influence on Scots Gaelic is often indicated by considering Irish language usage, which is not likely to have been influenced so much by Brittonic. In particular, the word srath (anglicised as "strath") is a native Goidelic word, but its usage appears to have been modified by the Welsh cognate ystrad whose meaning is slightly different. The effect on Irish has been the loan from British of many Latin-derived words. This has been associated with the Christianisation of Ireland from Britain.