foil

¹ American  

[foil] / fɔɪl /

verb (used with object)

1. to prevent the success of; frustrate; balk.

   Loyal troops foiled his attempt to overthrow the government.

   Synonyms:

   hamper, impede, thwart

2. to keep (a person) from succeeding in an enterprise, plan, etc.

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noun

1. Archaic. a defeat; check; repulse.

foil ² American  

[foil] / fɔɪl /

noun

1. metal in the form of very thin sheets.

   aluminum foil.

2. 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.

   Synonyms:

   counterpart, complement, contrast

5. Architecture. an arc or a rounded space between cusps, as in the tracery of a window or other ornamentation.

6. an airfoil or hydrofoil.

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verb (used with object)

1. to cover or back with foil.

2. to set off by contrast.

foil ³ American  

[foil] / fɔɪl /

noun

Fencing.

1. a flexible four-sided rapier having a blunt point.

2. 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.

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foil ¹ British  

/ 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. architect a small arc between cusps, esp as used in Gothic window tracery

6. short for aerofoil hydrofoil

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verb

1. to back or cover with foil

2. Also: foliate.  architect to ornament (windows) with foils

foil ² British  

/ fɔɪl /

verb

1. to baffle or frustrate (a person, attempt, etc)

2. hunting (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. archaic to repulse or defeat (an attack or assailant)

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noun

1. hunting any scent that obscures the trail left by a hunted animal

2. archaic a setback or defeat

foil ³ British  

/ fɔɪl /

noun

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

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Other Word Forms

• foilable
  adjective
• unfoilable
  adjective

Etymology

Origin of foil¹

First recorded in 1250–1300; Middle English foilen, fuylen “to trample, oppress, torment, mortify (the flesh),” irregular variant of fullen “to trample, full (cloth),” from Anglo-French foller, Old French fuler, from Vulgar Latin fullāre, from Latin fullō “fuller, launderer”; see full ²

Origin of foil²

First recorded in 1350–1400; Middle English foil, foille “leaf (of a plant or a book),” from Old French fuelle, fueille, foille (from Latin folia “leaves,” reinterpreted as a feminine singular noun) and from Old French fuel, fueil, foil (from Latin folium “leaf of a plant, blade”)

Origin of foil³

First recorded in 1585–95; origin uncertain

Explanation

You can serve as a foil to someone if you show them to be better than you by contrast. If you can't dance but your friend Lisa can, you can be a foil to Lisa's grace. If you're having trouble remembering this definition, think about a shiny piece of tin foil. It reflects an image back to you, so if you're a foil to someone, their image is reflected off of you in a positive light. Your brother's mediocre grades might serve as a foil to your intelligence. As a verb, if you foil someone's plans or attempts to do something, you cause them to fail. Your brother will be really mad if you foil his plans to hide his mediocre report card from your parents.

Example Sentences

See Examples For:

foil

Court records show informants helped foil the plot.

From The Wall Street Journal ● Sep. 20, 2026

The new Pokémon card set features new illustrated rare cards, as well as some with foil finishes.

From MarketWatch ● Sep. 17, 2026

We had a probably bit of aluminum foil and I had a funnel.

From Los Angeles Times ● Sep. 5, 2026

Across the French capital, where few homes have air conditioning, desperate locals had taped foil survival blankets over their windows, hoping to keep out the fierce sun.

From Barron's ● Aug. 25, 2026

Preheat the oven to 275°F. Line two cookie sheets with aluminum foil and spray with nonstick cooking spray.

From "Hope Springs" by Jaime Berry

Related Words

• counter
• curb
• elude
• frustrate
• hinder
• nullify
• prevent
• thwart