Forfeda
The forfeda (sing. "forfid") are the "additional" letters of the Ogham alphabet, beyond the basic inventory of twenty signs. Their name derives from "fid" ("wood", a term also used for Ogham letters) and the prefix "for-" ("additional"). The most important of these are five "forfeda" which were arranged in their own "aicme" or class, and were invented in the Old Irish period, several centuries after the peak of Ogham usage. They appear to have represented sounds felt to be missing from the original alphabet, maybe "é(o)", "ó(i)", "ú(i)", "p" and "ch". The "aicme" forfeda. The five "aicme" forfeda are  glossed in the manuscripts "Auraicept na n-Éces" ('The Scholars' Primer), "De dúilib feda" ('Elements of the Letters') and "In Lebor Ogaim" ('The Book of Ogam'), by several "Bríatharogaim" ("word oghams" ), or two word kennings, which explain the meanings of the names of the letters of the Ogham alphabet. Three variant lists of "bríatharogaim" or 'word-oghams' have been preserved, dating to the Old Irish period. They are as follows: Later Medieval scholars believed that all of the letter names of the ogham alphabet were those of trees, and attempted to explain the "bríatharogaim" in that light. However, modern scholarship  has shown that only eight at most of the original twenty letter names are those of trees, and that the word-oghams or kennings themselves support this. Of the "forfeda" letter names, only one may be that of a tree or shrub (pín) and their kennings as edited (in normalized Old Irish) and translated by McManus (1988) are as follows: Four of these names are glossed in the Auraicept with tree names, as "aspen", as "spindle-tree or ivy", as "honeysuckle", and as "gooseberry or thorn". The kennings for "Ébhadh" point to the sound "éo" or "é", which is also  the word for "salmon". The name appears modelled after "Eadhadh" and "Iodhadh". The kennings for "Ór" point to the word "ór" "gold" (cognate to Latin "aurum"). The kenning of "Uilleann", "great elbow", refers to the letter name. Since the Ogham alphabet dates to the Primitive Irish period, it had no sign for [p] in its original form and the letter "Pín" was added as a letter to express it. McManus states that the name "Pín" was probably influenced by Latin "pinus" ('pine'), but a more likely explanation is that it derives from Latin "spina" ('thorn'), as the kennings indicate a  tree or shrub with sweet tasting fruit (therefore not a pine). According to Kelly (1976) the name "spín" ( deriving from the Latin ) appears in the Old Irish tree lists as meaning either gooseberry or thorn, so the medieval glosses may be correct on this occasion. The name "Eamhancholl" means "twinned "coll"", referring to the shape of the letter (ᚙ resembling two ᚉ), and also perhaps referring to its sound being similar to that of "coll" ( being a fricative variant of ). The Bríatharogam kenning "groan of a sick person" refers to a value "ch" [x], predating the decision that all five  forfeda represent vowels. Apart from the first letter, the forfeda were little used in inscriptions, and this led later oghamists to rearrange them as a series of vowel diphthongs, necessitating a complete change to the sounds of "Pín" and "Eamhancholl" (the name "Pín" also had to be changed to "Iphín"). This arrangement is how they appear in most manuscripts: This arrangement meant that once again the ogham alphabet was without a letter for the [p] sound, making necessary the creation of Peith (see below). Inscriptions. Apart from the first letter "Eabhadh", the "forfeda" do not appear often in orthodox ogham  inscriptions. "Eabhadh" was in fact frequently used as part of the formula word KOI ᚕᚑᚔ, but with the value /k/ or /x/. KOI means something like 'here' and is the ogham equivalent of the Latin "hic iacet" (McManus §5.3, 1991); it is etymologically linked with the Latin "cis" ("on this side"). It also appears with its vocalic value in later orthodox inscriptions however. Of the other "forfeda" the next three appear only a few times, and the last letter "Eamhancholl" does not appear at all. So rare are the other "forfeda" in inscriptions that it is worthwhile detailing the individual  examples (numbering as given by Macalister): Other forfeda. Beyond the five Forfeda discussed above, which doubtlessly date to Old Irish times, there is a large number of letter variants and symbols, partly found in manuscripts, and partly in "scholastic" (post 6th century) inscriptions collectively termed "Forfeda". They may date to Old Irish, Middle Irish or even early modern times. Peith. Due to the "schematicism of later Ogamists" (McManus 1988:167), who insisted on treating the five primary forfeda as vowels, [p] had again to be expressed as a modification of [b], called , after "beithe", also called "beithe bog" "soft "beithe"" or , tautologically, "peithbog" (ᚚ "Peith", Unicode allocation U+169A). Manuscript tradition. The 7th-12th century "Auraicept na n-Éces" among the 92 "variants" of the Ogham script gives more letters identified as "forfeda" (variant nrs. 79, 80 and 81). Inscriptions. The Bressay stone in Shetland (CISP BREAY/1) contains five forfeda, three of them paralleled on other Scottish monuments and also in Irish manuscripts, and two unique to Bressay. One of the latter is possibly a correction of an error in carving and not intended as a forfid. One is "rabbit-eared", interpreted as some kind of modified D, presumably the voiced spirant. Another  is an "angled vowel", presumably a modified A. One unique character consists of five undulating strokes sloping backwards across the stem, possibly a modified I. The fourth is a four-stroke cross-hatching, also appearing in the late eighth or ninth-century Bern ogham alphabet and syllabary under a label which has previously been read as RR, but another suggestions is SS. It appears in the Book of Ballymote, scale no. 64.CISP - BREAY/1