foil

1. A very thin sheet of metal. (countable, uncountable)
2. A very thin sheet of plastic. (countable, uncountable)
3. Thin aluminium/aluminum (or, formerly, tin) used for wrapping food. (uncountable) · wrap the sandwich up in foil
4. A thin layer of metal put between a jewel and its setting to make it seem more brilliant. (countable, uncountable)
5. 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. (countable, figuratively, uncountable)
6. Anything that acts by contrast to emphasise the characteristics of something. (countable, figuratively, uncountable) · 1725-1726, William Broome, The Odyssey Hector has also a foil to set regard
7. A very thin sword with a blunted (or foiled) tip. (countable, uncountable) · 1784-1810, William Mitford, History of Greece Socrates contended with a foil against Demosthenes with a sword.
8. A thin, transparent plastic material on which marks are made and projected for the purposes of presentation. See transparency. (countable, uncountable)

Plural foils