foil (v.1)

c. 1300, foilen "to spoil a trace or scent by running over it" (more commonly defoilen), irregularly from Old French foler, fuler "trample on, injure, maim; ill-treat, deceive, get the better of" (13c., Modern French fouler), from Vulgar Latin *fullare "to clean cloth" (by treading on it), from Latin fullo "one who cleans cloth, a fuller," which is of unknown origin. Compare full (v.).

Hence, "to overthrow, defeat" (1540s; as a noun in this sense from late 15c.); "frustrate the efforts of" (1560s). Related: Foiled; foiling. Foiled again! as a cry of defeat and dismay is from at least 1847.

foil (n.)

"very thin sheet of metal," early 14c., foile, from Old French foil, fueill, fueille "leaf; foliage; sheet of paper; sheet of metal" (12c., Modern French fueille), from Latin folia, plural (mistaken for fem. singular) of folium "leaf" (from PIE root *bhel- (3) "to thrive, bloom").

The sense of "one who enhances another by contrast" (1580s) is from the practice of backing a gem with metal foil to make it shine more brilliantly. The meaning "light sword used in fencing" (1590s) could be from this sense, or from foil (v.). The sense of "metallic food wrap" is from 1897.

foil (v.2)

"apply foil to," 1610s, from foil (n.1).

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Definitions of foil from WordNet
foil (n.)
a piece of thin and flexible sheet metal;
the photographic film was wrapped in foil
foil (n.)
anything that serves by contrast to call attention to another thing's good qualities;
pretty girls like plain friends as foils
Synonyms: enhancer
foil (n.)
a device consisting of a flat or curved piece (as a metal plate) so that its surface reacts to the water it is passing through;
Synonyms: hydrofoil
foil (n.)
picture consisting of a positive photograph or drawing on a transparent base; viewed with a projector;
Synonyms: transparency
foil (n.)
a light slender flexible sword tipped by a button;
foil (v.)
enhance by contrast;
In this picture, the figures are foiled against the background
foil (v.)
hinder or prevent (the efforts, plans, or desires) of;
foil your opponent
Synonyms: thwart / queer / spoil / scotch / cross / frustrate / baffle / bilk
foil (v.)
cover or back with foil;
foil mirrors