A very thin sheet of metal. / (uncountable) Thin aluminium/aluminum (or, formerly, tin) used for wrapping food. / A thin layer of metal put between a jewel and its setting to make it seem more brilliant.

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

To prevent (something) from being accomplished. / To prevent (someone) from accomplishing something. / To blunt; to dull; to spoil. / (obsolete) To tread underfoot; to trample.

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

(hunting) The track of an animal.

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

(obsolete) To defile; to soil.

(mnemonic) An acronym for the algorithm for multiplying two binomials.

(transitive) To apply the FOIL algorithm to.

simple past tense and past participle of foil