(foil) v.t.
1. To prevent the success of; balk; frustrate; baffle.
2. In hunting, to cross and recross (a scent or trail) so as to confuse pursuers. See synonyms under BAFFLE, HINDER¹.
—noun
1. Archaic A thwarting; frustration.
2. In wrestling, an incomplete fall.
3. An animal's trail. [<OF fouler, fuler crush, trample down <LL fullare full cloth <fullo a fuller]

(foil) noun
1. Metal in very thin pliable sheets or leaves.
2. A leaf of bright metal placed by jewelers beneath an inferior gem to heighten the color or luster.
3. Anything serving to adorn or set off by contrast something different or superior.
4. The reflecting amalgam on the back of a mirror.
5. Archit. A leaflike division in ornamentation; a lobe, as in tracery. A group of three foils is called trefoil; of four, quatrefoil; of five, cinquefoil; etc.
6. Obs. A leaf.
—v.t.
1. To apply foil to; cover with foil.
2. To intensify or set off by contrast.
3. Archit. To adorn, as windows, with foils. [<OF <L folium leaf]
FOILS (def. 5)
Foliated tracery in Gothic window, Grace Church Chantry, New York.

(foil) noun
1. A blunted rapierlike implement, sometimes having a button on its end, used in fencing.
2. The art of fencing. [Origin uncertain]