foil

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

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, figurative) 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.
   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. December 20 2022, Leigh Monson, “Puss In Boots: The Last Wish review: Antonio Banderas leads the best film yet in the Shrek franchise”, in AV Club
5. (figurative) Anything that acts by contrast to emphasise the characteristics of something.
   1725-1726, William Broome, The Odyssey Hector has also a foil to set regard
6. (fencing) A very thin sword with a blunted (or foiled) tip
   1784-1810, William Mitford, History of Greece Socrates contended with a foil against Demosthenes with a sword.
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.
   I personally would collect all the foils from Base Set before this one, but the market is what the market is. 2016, Pojo's Unofficial Big Book of Pokémon, Triumph Books
9. (heraldry) A stylized flower or leaf.
10. (hydrodynamics, nautical) Clipping of hydrofoil.
11. (aerodynamics, aviation) Clipping of aerofoil/airfoil.

verb

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

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

1. To prevent (something) from being accomplished.
   They foiled my plans.
2. To prevent (someone) from accomplishing something.
   I was foiled by my superior
   First, former Toffee Mikel Arteta sent Walcott racing clear but instead of shooting he squared towards Ramsey, who was foiled by Tony Hibbert. December 10, 2011, David Ornstein, “Arsenal 1 - 0 Everton”, in BBC Sport
   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. August 20, 2017, “The Observer view on the attacks in Spain”, in The Observer
3. To blunt; to dull; to spoil.
4. (obsolete) To tread underfoot; to trample.
   King Richard […] caused the ensigns of Leopold to be pulled down and foiled underfoot. 1603, Richard Knolles, The Generall Historie of the Turkes

noun

1. Failure when on the point of attainment; defeat; frustration; miscarriage.
   Nor e'er was fate so near a foil. 1685, John Dryden, Threnodia Augustalis
2. One of the incorrect answers presented in a multiple-choice test.

Etymology 3

From French foulis.

noun

1. (hunting) The track of an animal.

Etymology 4

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

verb

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

Etymology 5

See file.

verb

1. (obsolete) To defile; to soil.