foil

UK: /ˈfɔɪl/ US: /fɔɪl/ ,(foil)

WordReference Random House Learner's Dictionary of American English © 2025

foil¹ /fɔɪl/   v. [~ + object]

1. to prevent the success of;
   thwart:
   Loyal troops foiled the revolt.

foil² /fɔɪl/   n. 

1. Metallurgy metal in very thin sheets:
   [uncountable] aluminum foil.
2. a person or thing that serves as a contrast to another:
   [countable] Goodness was a foil to their villainy.

See -foli-.
foil³ /fɔɪl/   n. 

1. Sport [countable] a flexible four-sided sword having a blunt point, used for fencing.

WordReference Random House Unabridged Dictionary of American English © 2025

foil¹  (foil), v.t. 

1. to prevent the success of;
   frustrate;
   balk:
   Loyal troops foiled his attempt to overthrow the government.
2. to keep (a person) from succeeding in an enterprise, plan, etc.

n. 

3. [Archaic.] a defeat;
   check;
   repulse.

• Anglo-French foller, Old French fuler to trample, full (cloth). See full²
• Middle English foilen, 1250–1300

foil′a•ble, adj. 
Synonyms

• 1. thwart; impede, hamper.

foil²  (foil), n. 

1. Metallurgy metal in the form of very thin sheets:
   aluminum foil.
2. Metallurgy the metallic backing applied to glass to form a mirror.
3. a thin layer of metal placed under a gem in a closed setting to improve its color or brilliancy.
4. a person or thing that makes another seem better by contrast:
   The straight man was an able foil to the comic.
5. Architecture an arc or a rounded space between cusps, as in the tracery of a window or other ornamentation.
6. Aeronautics an airfoil or hydrofoil.

v.t. 

7. to cover or back with foil.
8. to set off by contrast.

• Latin folium leaf, blade)
• Latin folia leaves), fuel, fueil, foil (
• Old French fuelle, fueille, foille (
• Middle English foille, foil 1350–1400

Synonyms

• 4. contrast, complement, counterpart.

foil³  (foil), n. [Fencing.]

1. Sport a flexible four-sided rapier having a blunt point.
2. Sport foils, the art or practice of fencing with this weapon, points being made by touching the trunk of the opponent's body with the tip of the weapon.

• origin, originally uncertain 1585–95

Collins Concise English Dictionary © HarperCollins Publishers::

foil / fɔɪl/ verb (transitive)

1. to baffle or frustrate (a person, attempt, etc)
2. (of hounds, hunters, etc) to obliterate the scent left by a hunted animal or (of a hunted animal) to run back over its own trail
3. to repulse or defeat (an attack or assailant)

Etymology: 13th Century foilen to trample, from Old French fouler, from Old French fuler tread down, full²

ˈfoilable adjective

foil / fɔɪl/ noun

1. metal in the form of very thin sheets: gold foil, tin foil
2. the thin metallic sheet forming the backing of a mirror
3. a thin leaf of shiny metal set under a gemstone to add brightness or colour
4. a person or thing that gives contrast to another
5. a small arc between cusps, esp as used in Gothic window tracery
6. short for aerofoil, hydrofoil

verb (transitive)

1. to back or cover with foil

Etymology: 14th Century: from Old French foille, from Latin folia leaves, plural of folium

foil / fɔɪl/ noun

1. a light slender flexible sword tipped by a button and usually having a bell-shaped guard

Etymology: 16th Century: of unknown origin