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.

---

verb (used without object)

foams, present (3rd person singular) foamed, past participle, past foaming present participle

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

verb (used with object)

foams, present (3rd person singular) foamed, past participle, past foaming present participle

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

---

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

---

Other Word Forms

Derived Forms

• foamer
  noun
• foamable
  adjective
• foamless
  adjective
• foamlike
  adjective
• unfoamed
  adjective
• unfoaming
  adjective
• foamingly
  adverb

Inflected Forms

Participles

• foaming
  present
• foamed
  past

Conjugated Forms

Present

• foam
  simple
• foams
  simple
• have foamed
  perfect
• has foamed
  perfect
• am foaming
  progressive
• are foaming
  progressive
• is foaming
  progressive
• have been foaming
  perfect progressive
• has been foaming
  perfect progressive

Past

• foamed
  simple
• had foamed
  perfect
• was foaming
  progressive
• were foaming
  progressive
• had been foaming
  perfect progressive

Future

• will foam
  simple
• will have foamed
  perfect
• will be foaming
  progressive
• will have been foaming
  perfect progressive

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

Over the next week, the fire continued to burn through dense insulation foam within the building’s walls and other unknown industrial materials, blanketing much of L.A. in acrid smoke.

From Los Angeles Times • Jun. 30, 2026

Much of the disaster site was covered with small pellets of white foam.

From The Wall Street Journal • Jun. 28, 2026

Modern balls often have multiple layers, including "a bladder, then a textile layer, then foam and another few layers like that," said Phillips.

From BBC • Jun. 27, 2026

Thick foam from the building’s insulation floated by on streams that leaked from the hulking shell, which firefighters have been drenching for days since the fire erupted on the roof the afternoon of June 17.

From Los Angeles Times • Jun. 25, 2026

Usually, when we make a mistake like that on bars, we fall safely into the spongy foam underneath.

From "Courage to Soar" by Simone Biles

Related Words

• cream
• froth
• spray