I. foil 1 /fɔɪl/ BrE AmE noun
[ Date: 1300-1400 ; Language: Old French ; Origin: Latin folium 'leaf' ]
1 . [uncountable] metal sheets that are as thin as paper, used for wrapping food
silver/aluminium/kitchen foil
Cover the chicken with silver foil and bake.
⇨ ↑ tinfoil
2 . [uncountable] paper that is covered with very thin sheets of metal:
chocolates in foil wrappers
3 . be a foil to/for somebody/something to emphasize the good qualities of another person or thing, by being very different from them:
The simple stone floor is the perfect foil for the brightly coloured furnishings.
4 .
[countable] a light narrow sword used in ↑ fencing
II. foil 2 BrE AmE verb [transitive often passive]
[ Date: 1300-1400 ; Language: French ; Origin: fouler 'to step on' ]
to prevent something bad that someone is planning to do:
A massive arms-smuggling plan has been foiled by the CIA.