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."

Definitions of foam

n a mass of small bubbles formed in or on a liquid

“the beer had a thick head of foam
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shaving foam
toiletry consisting of a liquid preparation containing many small bubbles that soften the beard before shaving
the foam or froth that accumulates at the top when you pour an effervescent liquid into a container
the foam resulting from excessive sweating (as on a horse)
lather, soapsuds, suds
the froth produced by soaps or detergents
foam or froth on the sea
white water, whitewater
frothy water as in rapids or waterfalls
shaving cream, shaving soap
toiletry consisting of a preparation of soap and fatty acids that forms a rich lather for softening the beard before shaving
Type of:
a hollow globule of gas (e.g., air or carbon dioxide)

n a lightweight material in cellular form; made by introducing gas bubbles during manufacture

a light resilient foam of polystyrene
foam rubber
spongy rubber; made by introducing air bubbles before vulcanization and used for cushioning or upholstery
Type of:
material, stuff
the tangible substance that goes into the makeup of a physical object

v become bubbly or frothy or foaming

“The river was foaming
effervesce, fizz, form bubbles, froth, sparkle
form a lather
foam as if boiling
Type of:
form, produce, or emit bubbles

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