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

Together, the two airlines said, they would pose a better foil to the giants United, American, and Delta, which had formed over the decades through their own big piles of mergers and acquisitions.

From Slate • May 5, 2026

Wrap them in foil and store them in the fridge.

From Salon • May 5, 2026

The prices of other Karex products, from personal lubricants and probe covers to catheters and aluminium foil packaging, have also increased, Goh said.

From Barron's • Apr. 24, 2026

She also said her message of competency and experience wasn’t resonating among voters who were seeking a fiery foil to President Trump, not “Boring Betty,” as she dubbed herself.

From Los Angeles Times • Apr. 20, 2026

I drop my foil, trying to break my fall.

From "Black Brother, Black Brother" by Jewell Parker Rhodes

Related Words

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