Foil

1. noun

   a piece of thin and flexible sheet metal

   “the photographic film was wrapped in foil”

2. noun

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

   “pretty girls like plain friends as foils”

   Similar: enhancer

3. 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”

   Similar: hydrofoil