foam
Americannoun
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a collection of minute bubbles formed on the surface of a liquid by agitation, fermentation, etc..
foam on a glass of beer.
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the froth of perspiration, caused by great exertion, formed on the skin of a horse or other animal.
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froth formed from saliva in the mouth, as in epilepsy and rabies.
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a thick frothy substance, as shaving cream.
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(in firefighting)
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a chemically produced substance that smothers the flames on a burning liquid by forming a layer of minute, stable, heat-resistant bubbles on the liquid's surface.
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the layer of bubbles so formed.
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a dispersion of gas bubbles in a solid, as foam glass, foam rubber, polyfoam, or foamed metal.
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Literary. the sea.
verb (used without object)
verb (used with object)
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to cause to foam.
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to cover with foam; apply foam to.
to foam a runway before an emergency landing.
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to insulate with foam.
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to make (plastic, metal, etc.) into a foam.
idioms
noun
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a mass of small bubbles of gas formed on the surface of a liquid, such as the froth produced by agitating a solution of soap or detergent in water
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frothy saliva sometimes formed in and expelled from the mouth, as in rabies
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the frothy sweat of a horse or similar animal
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any of a number of light cellular solids made by creating bubbles of gas in the liquid material and solidifying it: used as insulators and in packaging
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( as modifier )
foam rubber
foam plastic
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a colloid consisting of a gas suspended in a liquid
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a mixture of chemicals sprayed from a fire extinguisher onto a burning substance to create a stable layer of bubbles which smothers the flames
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a poetic word for the sea
verb
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to produce or cause to produce foam; froth
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(intr) to be very angry (esp in the phrase foam at the mouth )
Other Word Forms
Etymology
Origin of foam
before 900; Middle English fom, Old English fām; cognate with German Feim
Explanation
Foam is a substance with so many tiny air bubbles that it becomes frothy or thick. Your liquid shampoo becomes a foam as you lather it into your wet hair. There's a layer of foam on top of your root beer float, and shaving cream usually comes out of its can in the form of foam. When something froths up this way, you can say that it foams, like turbulent ocean water or a bubble bath that grows as you add water to the tub. The Old English root word is fam, which means "foam," but also "saliva froth" and "sea."
Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
A grandmother who paid rogue builders more than £13,000 to remove spray foam insulation from her house has said it has left her feeling "trapped" with a leaking roof which will cost £20,000 to repair.
From BBC • May 10, 2026
Pistachio cold foam now perches atop iced coffees from nationwide chains, Dubai chocolate knock-offs sit at every grocery checkout stand and boutique patisseries fill croissants with pistachio butters and creams.
From Salon • May 6, 2026
Get them a gift that matches their path: from a foam roller for the wellness coach to a stylish smock for the aspiring pop-up chef.
From The Wall Street Journal • Apr. 28, 2026
The improvement came primarily from reducing the shoe’s weight by 30% to 3.4 ounces for a men’s size 9 by re-engineering carbon fiber and foam.
From Los Angeles Times • Apr. 27, 2026
During a commercial break, I hustled to the hall bathroom to wet and comb antifrizz foam through my hair.
From "Hope Springs" by Jaime Berry
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
