Definition of "Foil" :

noun: a light slender flexible sword tipped by a button

noun: a piece of thin and flexible sheet metal

"The photographic film was wrapped in foil."

noun: picture consisting of a positive photograph or drawing on a transparent base; viewed with a projector

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

"The fins of a fish act as hydrofoils."

noun: anything that serves by contrast to call attention to another thing's good qualities

"Pretty girls like plain friends as foils."

verb: cover or back with foil

"Foil mirrors."

verb: hinder or prevent (the efforts, plans, or desires) of

"Foil your opponent."

verb: enhance by contrast

"In this picture, the figures are foiled against the background."