foil1 / foil/ • v. [tr.] prevent (something considered wrong or undesirable) from succeeding: a brave policewoman foiled the armed robbery. ∎ frustrate the efforts or plans of: Errol Flynn was a dashing Mountie foiling Nazi agents in Canada. ∎ Hunting (of a hunted animal) run over or cross (ground or a scent or track) in such a way as to confuse the hounds.• n. 1. Hunting the track or scent of a hunted animal.2. archaic a setback in an enterprise; a defeat.foil2 • n. 1. metal hammered or rolled into a thin flexible sheet, used chiefly for covering or wrapping food: aluminum foil.2. a person or thing that contrasts with and so emphasizes and enhances the qualities of another: the earthy taste of grilled vegetables is a perfect foil for the tart bite of creamy goat cheese. ∎ a thin leaf of metal placed under a precious stone to increase its brilliance.3. Archit. a leaf-shaped curve formed by the cusping of an arch or circle, typically occurring in groups of three or more in Gothic tracery.foil3 • n. a light fencing sword without cutting edges but with a button on its point. ∎ the sport of fencing with a foil: for épée and foil, hits must be made with the point.DERIVATIVES: foil·ist / -ist/ n.foil4 • n. each of the winglike structures fitted to a hydrofoil's hull to lift it clear of the water at speed.