foam

American  

[fohm] / foʊm /

noun

1. a collection of minute bubbles formed on the surface of a liquid by agitation, fermentation, etc..

   foam on a glass of beer.

   Synonyms:

   scum, fizz, head, spume, froth

2. the froth of perspiration, caused by great exertion, formed on the skin of a horse or other animal.

3. froth formed from saliva in the mouth, as in epilepsy and rabies.

4. a thick frothy substance, as shaving cream.

5. (in firefighting)

   1. 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.

   2. the layer of bubbles so formed.

6. a dispersion of gas bubbles in a solid, as foam glass, foam rubber, polyfoam, or foamed metal.

7. Literary. the sea.

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verb (used without object)

1. to form or gather foam; emit foam; froth.

verb (used with object)

1. to cause to foam.

2. to cover with foam; apply foam to.

   to foam a runway before an emergency landing.

3. to insulate with foam.

4. to make (plastic, metal, etc.) into a foam.

idioms

1. foam at the mouth, to be extremely or uncontrollably angry.

foam British  

/ fəʊm /

noun

1. 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

2. frothy saliva sometimes formed in and expelled from the mouth, as in rabies

3. the frothy sweat of a horse or similar animal

4. 1. 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

   2. ( as modifier )

      foam rubber

      foam plastic

5. a colloid consisting of a gas suspended in a liquid

6. a mixture of chemicals sprayed from a fire extinguisher onto a burning substance to create a stable layer of bubbles which smothers the flames

7. a poetic word for the sea

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verb

1. to produce or cause to produce foam; froth

2. (intr) to be very angry (esp in the phrase foam at the mouth )

foam Scientific  

/ fōm /

1. Small, frothy bubbles formed in or on the surface of a liquid, as from fermentation or shaking.

2. A colloid in which particles of a gas are dispersed throughout a liquid.

3. Compare aerosol emulsion

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Other Word Forms

• defoam verb (used with object)
• foamable adjective
• foamer noun
• foamingly adverb
• foamless adjective
• foamlike adjective
• unfoamed adjective
• unfoaming adjective

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

They are present in minute quantities in many products including non-stick cookware, cardboard food packaging, textiles, firefighting foam, paint and more.

From The Wall Street Journal • Apr. 15, 2026

Across from the booth and above the bar, a pink-and-white television made from an iPad inside a plastic foam cooler plays old cereal commercials and clips from “I Love Lucy” and “Bewitched” on repeat.

From Los Angeles Times • Apr. 15, 2026

Prosecutors believe the fire started when champagne bottles with sparklers attached were raised too close to the ceiling in the bar's basement level, igniting the sound insulation foam.

From Barron's • Apr. 8, 2026

Common insulation materials include fibreglass, non-combustible mineral wool, foam boards and natural fibre such as wood or cork.

From BBC • Mar. 25, 2026

The toothpaste fills my mouth with soft, sweet foam.

From "Born Behind Bars" by Padma Venkatraman

Related Words

• cream
• froth
• spray