# foil
## English
### Pronunciation

* IPA: /fɔɪl/
* Audio (US):(file)
* Rhymes: -ɔɪl

### Etymology 1

From Middle English foyle, from Middle French fueille, from Old French fueille (“plant leaf”), from Late Latin folia, the plural of folium, mistaken as a singular feminine.
The literary sense is from the practice of backing a gem with metal foil to make it shine more brilliantly.
Doublet of folio and folium, distantly also with phyllo and phyllon.

#### Noun

foil (countable and uncountable, plural foils)
* A very thin sheet of metal.
* (chiefly uncountable) Thin aluminium/aluminum (or, formerly, tin) used for wrapping food.
    wrap the sandwich up in foil
* A thin layer of metal put between a jewel and its setting to make it seem more brilliant.
* (authorship, figuratively) In literature, theatre/theater, etc., a character who helps emphasize the traits of the main character and who usually acts as an opponent or antagonist, but can also serve as the sidekick of the protagonist.
** 2022 December 20, Leigh Monson, “Puss In Boots: The Last Wish review: Antonio Banderas leads the best film yet in the Shrek franchise”, in AV Club‎:As Puss comes to realize his legendary status is not a substitute for interpersonal connection, his interactions with Kitty and the therapy dog start to take on a surprising amount of weight, while Goldilocks serves as a well-realized foil who has more in common with Puss that is at first apparent.
* (figuratively) Anything that acts by contrast to emphasise the characteristics of something.
** a. 1587, Philippe Sidnei [i.e., Philip Sidney], “(please specify the folio)”, in [Fulke Greville; Matthew Gwinne; John Florio], editors, The Countesse of Pembrokes Arcadia [The New Arcadia], London: […] [John Windet] for William Ponsonbie, published 1590, →OCLC:As she a black silk cap on him begun / To set, for foil of his milk-white to serve.
** 1725-1726, William Broome, The Odyssey
    Hector has also a foil to set regard
* (fencing) A very thin sword with a blunted (or foiled) tip
** 1598–1599 (first performance), William Shakespeare, “Much Adoe about Nothing”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, →OCLC, [Act V, scene ii]:Blunt as the fencer's foils, which hit, but hurt not.
** 1784-1810, William Mitford, History of Greece
    Socrates contended with a foil against Demosthenes with a sword.
* A thin, transparent plastic material on which marks are made and projected for the purposes of presentation. See transparency.
* A premium trading card with a glossy finish.
** 2016, Pojo's Unofficial Big Book of Pokémon, Triumph Books:I personally would collect all the foils from Base Set before this one, but the market is what the market is.
* (heraldry) A stylized flower or leaf.
* (hydrodynamics, nautical) Clipping of hydrofoil.
* (aerodynamics, aviation) Clipping of aerofoil/airfoil.

##### Synonyms

* (thin aluminium/aluminum): aluminium foil, silver foil, silver paper, tin foil

##### Derived terms

* aluminum foil
* biofoil
* blisterfoil
* bow foil
* cephalofoil
* cinquefoil
* counterfoil
* dufoil
* F50
* featherfoil
* foilboard
* foilist
* foilsman
* foil stone
* holofoil
* jetfoil
* octofoil
* quatrefoil
* rockfoil
* rushfoil
* sexfoil
* tinfoil
* tin foil
* trefoil
* twifoil

##### Translations
#### Verb

foil (third-person singular simple present foils, present participle foiling, simple past and past participle foiled)
* (transitive) To cover or wrap with foil.
* (nautical) Clipping of hydrofoil.

##### Translations
### Etymology 2

From Middle English foilen (“spoil a scent trail by crossing it”), from Old French fouler (“tread on, trample”), ultimately from Latin fullō (“I trample, I full”).

#### Verb

foil (third-person singular simple present foils, present participle foiling, simple past and past participle foiled)
* To prevent (something) from being accomplished.
    They foiled my plans.
* To prevent (someone) from accomplishing something.
    I was foiled by my superior
** 1606, Caius [i.e., Gaius] Suetonius Tranquillus, “The Historie of Flavius Vespatianus Augustus”, in Philêmon Holland, transl., The Historie of Twelve Cæsars Emperours of Rome. […], London: […] [Humphrey Lownes and George Snowdon] for Matthew Lownes, →OCLC, section 5, page 243:And at the field fought before Bebriacum, ere the battailes joyned, tvvo Ægles had a conflict and bickered together in all their fights: and vvhen the one of them was foyled and overcome, a third came at the very inſtant from the ſunne riſing and chaſed the Victreſſe avvay.
** 1697, Virgil, “The Seventh Book of the Æneis”, in John Dryden, transl., The Works of Virgil: Containing His Pastorals, Georgics, and Æneis. […], London: […] Jacob Tonson, […], →OCLC:And by mortal man at length am foil'd.
** 1812, Lord Byron, “Canto I”, in Childe Harold’s Pilgrimage. A Romaunt, London: Printed for John Murray, […]; William Blackwood, Edinburgh; and John Cumming, Dublin; by Thomas Davison, […], →OCLC, stanza LV:her long locks that foil the painter's power
** 1848 November – 1850 December, William Makepeace Thackeray, chapter 28, in The History of Pendennis. […], volume (please specify |volume=I or II), London: Bradbury and Evans, […], published 1849–1850, →OCLC:Perhaps you think you love me now but it is only for an instant, and because you are foiled.
** 2011 December 10, David Ornstein, “Arsenal 1 - 0 Everton”, in BBC Sport‎:First, former Toffee Mikel Arteta sent Walcott racing clear but instead of shooting he squared towards Ramsey, who was foiled by Tony Hibbert.
** 2017 August 20, “The Observer view on the attacks in Spain”, in The Observer‎:Many jihadist plots have been foiled and the security apparatus is getting better, overall, at pre-empting those who would do us ill. But, they say, the nature of the threat and the terrorists’ increasing use of low-tech, asymmetrical tactics such as hire vehicles and knives, make it all but impossible to stop every assault.
* To blunt; to dull; to spoil.
** 1711 August 11 (Gregorian calendar), [Joseph Addison], “TUESDAY, July 31, 1711”, in The Spectator, number (please specify the issue number); republished in Alexander Chalmers, editor, The Spectator; a New Edition, […], volume (please either specify the issue number or |volume=I to VI), New York, N.Y.: D[aniel] Appleton & Company, 1853, →OCLC:they foil the scent of one another.The spelling has been modernized.
* (obsolete) To tread underfoot; to trample.
** 1603, Richard Knolles, The Generall Historie of the Turkes:King Richard […] caused the ensigns of Leopold to be pulled down and foiled underfoot.
** 1596, Edmund Spenser, “Book V, Canto XXXIII”, in The Faerie Queene. […], London: […] [John Wolfe] for William Ponsonbie, →OCLC:Whom he did all to pieces breake and foyle, / In filthy durt, and left so in the loathely soyle.

##### Synonyms

* (prevent from being accomplished): put the kibosh on, scupper, thwart

##### Derived terms

* foilable
* foiler
* unfoiled

##### Translations
#### Noun

foil (plural foils)
* Failure when on the point of attainment; defeat; frustration; miscarriage.
** 1671, John Milton, “(please specify the page)”, in Paradise Regain’d. A Poem. In IV Books. To which is Added, Samson Agonistes, London: […] J[ohn] M[acock] for John Starkey […], →OCLC:Fame is no plant that grows on mortal foil
** 1685, John Dryden, Threnodia Augustalis:Nor e'er was fate so near a foil.
* One of the incorrect answers presented in a multiple-choice test.

### Etymology 3

From French foulis.

#### Noun

foil (plural foils)
* (hunting) The track of an animal.
** 1749, Henry Fielding, chapter IV, in The History of Tom Jones, a Foundling, volume (please specify |volume=I to VI), London: A[ndrew] Millar, […], →OCLC, book VII:[…] but after giving her a dodge, here's another b— follows me upon the foil.

##### Synonyms

* (track of an animal): spoor

##### Translations
### Etymology 4

From mnemonic acronym FOIL (“First Outside Inside Last”).

#### Verb

foil (third-person singular simple present foils, present participle foiling, simple past and past participle foiled)
* (mathematics) To expand a product of two or more algebraic expressions, typically binomials.

##### Translations
### Etymology 5

See file.

#### Verb

foil (third-person singular simple present foils, present participle foiling, simple past and past participle foiled)
* (obsolete) To defile; to soil.

### Etymology 6
#### Noun

foil (plural foils)
* (architecture) A small arc in the tracery of a window, etc.

##### Related terms

* multifoil
* polyfoil
* trefoil

### References

Douglas Harper (2001–2025) “foil”, in Online Etymology Dictionary.

### Anagrams

* Filo, LIFO, filo, lo-fi, lofi

## Old French
### Alternative forms

* feul
* foel
* fol
* fueill
* fuel
* fuil

### Etymology

From Latin folium. Compare fueille, from the plural of folium, folia.

### Noun

foil oblique singular, m (oblique plural fouz or foilz, nominative singular fouz or foilz, nominative plural foil)
* leaf (green appendage of a plant which photosynthesizes)

## Old Irish
### Etymology

From Proto-Celtic *uɸolexs, from *uɸo- (“under”) +‎ *leg- (“to lie”). Cognate with Welsh gwâl (“lair, pigsty”).

### Noun

foil f (genitive folach)
* ring, bracelet
** c. 845, St Gall Glosses on Priscian, published in Thesaurus Palaeohibernicus (reprinted 1975, Dublin Institute for Advanced Studies), edited and with translations by Whitley Stokes and John Strachan, vol. II, pp. 49–224, Sg. 64$^a$17
    foil ― glossing Latin armillam (“bracelet”)
* pigsty

#### Inflection

* $^H$ = triggers aspiration
* $^L$ = triggers lenition
* $^N$ = triggers nasalization

#### Derived terms

* muccfoil

#### Descendants

* Middle Irish: fail
** Irish: fail
** Scottish Gaelic: fail

### Mutation

Note: Certain mutated forms of some words can never occur in Old Irish. All possible mutated forms are displayed for convenience.

### References

* ↑ Matasović, Ranko (2009) “*ufo-leg-”, in Etymological Dictionary of Proto-Celtic (Leiden Indo-European Etymological Dictionary Series; 9), Leiden: Brill, →ISBN, page 398

### Further reading

* Gregory Toner, Sharon Arbuthnot, Máire Ní Mhaonaigh, Marie-Luise Theuerkauf, Dagmar Wodtko, editors (2019), “1 fail, foil”, in eDIL: Electronic Dictionary of the Irish Language
* Gregory Toner, Sharon Arbuthnot, Máire Ní Mhaonaigh, Marie-Luise Theuerkauf, Dagmar Wodtko, editors (2019), “1 foil, fail”, in eDIL: Electronic Dictionary of the Irish Language