foam

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A colloidal dispersion of a gas in a liquid or solid medium, such as shaving cream, foam rubber, or a substance used to fight fires. A foam may be produced, especially on the surface of a liquid, by agitation or by a chemical reaction, such as fermentation.
• noun Any of various light, porous, semirigid or spongy materials, usually the solidified form of a liquid full of gas bubbles, used as a building material or for thermal insulation or shock absorption, as in packaging.
• noun Frothy saliva produced especially as a result of physical exertion or a pathological condition.
• noun The frothy sweat of a horse or other equine animal.
• noun The sea.
• intransitive verb To produce or issue as foam; froth.
• intransitive verb To produce foam from the mouth, as from exertion or a pathological condition.
• intransitive verb To be extremely angry; rage.
• intransitive verb To teem; seethe.
• intransitive verb To cause to produce foam.
• intransitive verb To cause to become foam.

from The Century Dictionary.

• noun An aggregation of bubbles formed on the surface of water or other liquid by violent agitation or by fermentation; froth; spume: as, the foam of breaking waves; the foam of the mouth.
• noun The foaming sea; a foaming wave.
• noun Figuratively, foaming rage; fury.
• noun In mineralogy, same as aphrite.
• noun Scum, as from molten metal.
• To form or gather foam, as water (the crest of a wave), etc., from agitation, a liquor from fermentation, or the mouth from rage or disease; froth; spume.
• To become filled or covered with foam, as a steam-boiler when the water is frothy.
• To cause to foam; fill with something that foams; make frothy: as, to foam a tankard.
• To throw out with rage or violence: usually with out.

from the GNU version of the Collaborative International Dictionary of English.

• noun The white substance, consisting of an aggregation of bubbles, which is formed on the surface of liquids, or in the mouth of an animal, by violent agitation or fermentation; froth; spume; scum.
• noun in steam boilers, a cock at the water level, to blow off impurities.
• transitive verb To cause to foam; ; also (with out), to throw out with rage or violence, as foam.
• intransitive verb To gather foam; to froth.
• intransitive verb To form foam, or become filled with foam; -- said of a steam boiler when the water is unduly agitated and frothy, as because of chemical action.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A substance composed of a large collection of bubbles or their solidified remains.
• noun by extension sea foam; (figuratively) the sea.
• verb To form or emit foam.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a lightweight material in cellular form; made by introducing gas bubbles during manufacture
• verb become bubbly or frothy or foaming
• noun a mass of small bubbles formed in or on a liquid