foil

noun16

1. •
   A very thin sheet of metal.
2. •
   A very thin sheet of plastic.
3. •
   Thin aluminium/aluminum (or, formerly, tin) used for wrapping food.
4. •
   A thin layer of metal put between a jewel and its setting to make it seem more brilliant.
5. •
   A thin, transparent plastic material on which marks are made and projected for the purposes of presentation. See transparency.
6. •
   (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.
7. •
   (figurative) Anything that acts by contrast to emphasise the characteristics of something.

   • As she a black silk cap on him begun / To set, for foil of his milk-white to serve. — 1587
8. •
   A very thin sword with a blunted (or foiled) tip.

   • Blunt as the fencer's foils, which hit, but hurt not. — 1598
9. •
   Clipping of hydrofoil.
10. •
    Clipping of aerofoil/airfoil.
11. •
    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
12. •
    One of the incorrect answers presented in a multiple-choice test.
13. •
    Failure when on the point of attainment; defeat; frustration; miscarriage.

    • Fame is no plant that grows on mortal foil — 1671
14. •
    A stylized flower or leaf.
15. •
    A small arc in the tracery of a window, etc.
16. •
    The track of an animal.

    • […]but after giving her a dodge, here's another b— follows me upon the foil. — 1749

verb8

1. •
   To prevent (something) from being accomplished.

   • They foiled my plans.
2. •
   To prevent (someone) from accomplishing something.

   • I was foiled by my superior
3. •
   To cover or wrap with foil.
4. •
   To expand a product of two or more algebraic expressions, typically binomials.
5. •
   To blunt; to dull; to spoil.

   • they foil the scent of one another. — 1711
6. •
   Clipping of hydrofoil.
7. •
   (no longer used) To tread underfoot; to trample.

   • King Richard […] caused the ensigns of Leopold to be pulled down and foiled underfoot. — 1603
8. •
   (no longer used) To defile; to soil.

verb1

1. •
   To apply the FOIL algorithm to.