foil (Noun) — A piece of thin and flexible sheet metal. ex. "the photographic film was wrapped in foil"
foil (Noun) — Anything that serves by contrast to call attention to another thing's good qualities. ex. "pretty girls like plain friends as foils"
foil (Noun) — A device consisting of a flat or curved piece (as a metal plate) so that its surface reacts to the water it is passing through. ex. "the fins of a fish act as foils"
foil (Noun) — Picture consisting of a positive photograph or drawing on a transparent base; viewed with a projector.
foil (Noun) — (fencing) a light slender flexible sword tipped by a button.
foil (Verb) — Enhance by contrast. ex. "In this picture, the figures are foiled against the background"
foil (Verb) — Hinder or prevent (the efforts, plans, or desires) of. ex. "foil your opponent"
foil (Verb) — Cover or back with foil. ex. "foil mirrors"