foil

Foil is a term with several related meanings across materials, arts, and language. It most commonly denotes a thin sheet of metal, but it also names a fencing weapon, a literary device, and a verb meaning to thwart a plan. In addition, the word describes a decorative metal leaf and a conductive layer used in electronics.

Metal foil is produced by rolling metal to very small thicknesses. Aluminum foil is the best known for household use, but foils of gold, copper, and other metals are used in packaging, insulation, shielding, and art. Typical household aluminum foil is about 0.016 millimeters thick. Foils can also be used as electrodes in capacitors and other electronic components.

Foil in fencing is a lightweight weapon designed for thrusting. The blade is flexible, and points score when the tip makes contact on a valid target area, typically the torso, with rules determining who has right of way. Foil competition differs from epee and saber in target area and timing rules, and players wear masks, jackets, and other protective gear.

Literary foil is a character whose traits contrast with those of another character, usually to highlight particular qualities. The foil is not necessarily an antagonist; rather, the juxtaposition clarifies attributes such as courage, honesty, or temperament. Classic examples include a noble hero contrasted with a flawed sidekick in various works.

To foil means to prevent someone from achieving a goal or completing a plan. The term can be used in everyday language and journalism, such as reporting that a scheme was foiled by investigators.