- 1to stop something from happening, especially something illegal; to prevent someone from doing something synonym thwart
- 2 foil something to foil a plan/crime/plot Customs officials foiled an attempt to smuggle the paintings out of the country. foil somebody (in something) They were foiled in their attempt to smuggle the paintings.
NAmE//fɔɪl//[often passive]Verb Forms present simple I / you / we / they foil
he / she / it foils
past simple foiled
-ing form foiling