Emily Dickinson Lexicon

FOIL, v.t. [In Norm. afolee is rendered crippled; and afoula, damaged, wasted. If the primary or true literal sense is, to blunt, this word may be from the same root as fool; if to render vain, it would naturally be allied to fail.]

1. To frustrate; to defeat; to render vain or nugatory, as an effort or attempt. The enemy attempted to pass the river, but was foiled. He foiled his adversaries. And by a mortal man at length, am foiled. Dryden.
2. To blunt; to dull. When light wing'd toys / Of feathered Cupid foil. Shak.
3. To defeat; to interrupt, or to render imperceptible; as, to foil the scent in a chase. Addison.