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.

foil. In Gothic tracery any circular lobe tangent to the inner side of a larger arc or arch, meeting other lobes in points called cusps projecting inwards from the arch: prefixes are used to describe how many foils occur—trefoil (3), quatrefoil (4), cinquefoil (5), sexfoil (6), multifoil, etc. A quatrefoil, therefore, has four lobes, separated by cusps, in the shape of a flower with four leaves the axes of which are vertical and horizontal. Bands of quatrefoils were much used for enrichment during the Perpendicular period. When placed with the axes set diagonally, quatrefoils are called cross-quarters.

foil2 †leaf; thin sheet of metal XIV; thin leaf of metal placed under a precious stone to increase its brilliance, etc.; a thing that serves by contrast to set off another thing XVI.(i) — OF. foil :- L. folium leaf; (ii) — OF. foille (mod. feuille) :- L. folia, pl. of folium (n. pl. taken as fem. sg.).

foil1 tread under foot XIII; overthrow, discomfit, frustrate XVI. irreg. repr. (O)F. fouler :- Rom. *fullāre, f. L. fullō FULLER.

foil3 small sword with blunt edge and blunted point. XVI. of unkn. orig.