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See also: FOIL


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  • IPA(key): /fɔɪl/
  • (file)
  • Rhymes: -ɔɪl

Etymology 1[edit]

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.


foil (countable and uncountable, plural foils)

  1. A very thin sheet of metal.
  2. (chiefly uncountable) Thin aluminium/aluminum (or, formerly, tin) used for wrapping food.
    wrap the sandwich up in foil
  3. A thin layer of metal put between a jewel and its setting to make it seem more brilliant.
  4. (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[1]:
      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.
  5. (figuratively) Anything that acts by contrast to emphasise the characteristics of something.
  6. (fencing) A very thin sword with a blunted (or foiled) tip
  7. A thin, transparent plastic material on which marks are made and projected for the purposes of presentation. See transparency.
  8. 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.
  9. (heraldry) A stylized flower or leaf.
  10. (hydrodynamics, nautical) Clipping of hydrofoil.
  11. (aerodynamics, aviation) Clipping of aerofoil/airfoil.
Derived terms[edit]


foil (third-person singular simple present foils, present participle foiling, simple past and past participle foiled)

  1. (transitive) To cover or wrap with foil.
  2. (nautical) Clipping of hydrofoil.

Etymology 2[edit]

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).


foil (third-person singular simple present foils, present participle foiling, simple past and past participle foiled)

  1. To prevent (something) from being accomplished.
    They foiled my plans.
  2. To prevent (someone) from accomplishing something.
    I was foiled by my superior
    • 1606, C[aius, i.e., Gaius] Suetonius Tranquillus, “The Historie of Flavius Vespatianus Augustus”, in Philemon 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[2]:
      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[3]:
      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.
  3. To blunt; to dull; to spoil.
  4. (obsolete) To tread underfoot; to trample.


foil (plural foils)

  1. Failure when on the point of attainment; defeat; frustration; miscarriage.
  2. One of the incorrect answers presented in a multiple-choice test.

Etymology 3[edit]

From French foulis.


foil (plural foils)

  1. (hunting) The track of an animal.
  • (track of an animal): spoor

Etymology 4[edit]

From mnemonic acronym FOIL (First Outside Inside Last).


foil (third-person singular simple present foils, present participle foiling, simple past and past participle foiled)

  1. (mathematics) To expand a product of two or more algebraic expressions, typically binomials.

Etymology 5[edit]

See file.


foil (third-person singular simple present foils, present participle foiling, simple past and past participle foiled)

  1. (obsolete) To defile; to soil.


Douglas Harper (2001–2023), “foil”, in Online Etymology Dictionary.


Old French[edit]

Alternative forms[edit]


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


foil m (oblique plural fouz or foilz, nominative singular fouz or foilz, nominative plural foil)

  1. leaf (green appendage of a plant which photosynthesizes)

Old Irish[edit]


From Proto-Celtic *uɸolexs, from *uɸo- (under) +‎ leg- (to lie). Cognate with Welsh gwâl (lair, pigsty).[1]


foil f (genitive folach)

  1. 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. 64a17
      foilglossing Latin armillam (bracelet)
  2. pigsty


Feminine g-stem
Singular Dual Plural
Nominative foil folaigL folaig
Vocative foil folaigL foilgea
Accusative folaigN folaigL foilgea
Genitive folach folach folachN
Dative folaigL foilgib foilgib
Initial mutations of a following adjective:
  • H = triggers aspiration
  • L = triggers lenition
  • N = triggers nasalization

Derived terms[edit]


  • Middle Irish: fail


Old Irish mutation
Radical Lenition Nasalization
foil ḟoil foil
pronounced with /v(ʲ)-/
Note: Some of these forms may be hypothetical. Not every
possible mutated form of every word actually occurs.


  1. ^ 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[edit]