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”; 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

Back then, TV “friction” meant tweaking the rabbit ears with tin foil or asking your uncle to hold the antenna until the fourth quarter was done.

From The Wall Street Journal • Apr. 10, 2026

As a kid wandering the grocery store aisles with my mom, spotting the shiny green foil on the white O’Ryan’s boxes felt almost as exciting as presents from Santa on Christmas morning.

From Salon • Mar. 17, 2026

Instead, the company sent her at least a year’s worth of aluminum foil!

From MarketWatch • Mar. 10, 2026

Before me was a lunch as big and hefty as a brick, wrapped in gold-colored foil that gleamed with the promise of a delicious meal.

From Los Angeles Times • Feb. 19, 2026

“That aluminum foil lid is the greenhouse gases that are trapping heat in our atmosphere,” Mrs. Tally had explained.

From "Two Degrees" by Alan Gratz

Related Words

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