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
  1. noun
    a mass of small bubbles formed in or on a liquid
    synonyms: froth
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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)
  2. noun
    a lightweight material in cellular form; made by introducing gas bubbles during manufacture
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    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
  3. verb
    become bubbly or frothy or foaming
    “The river was foaming
    synonyms: effervesce, fizz, form bubbles, froth, sparkle
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    form a lather
    foam as if boiling
    type of:
    form, produce, or emit bubbles
Word Family

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