1. 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.
2. 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.
a. Frothy saliva produced especially as a result of physical exertion or a pathological condition.
b. The frothy sweat of a horse or other equine animal.
4. The sea.
v. foamed, foam·ing, foams
1. To produce or issue as foam; froth.
a. To produce foam from the mouth, as from exertion or a pathological condition.
b. To be extremely angry; rage: was foaming over the disastrous budget cuts.
3. To teem; seethe: a playground foaming with third graders.
1. To cause to produce foam.
2. To cause to become foam.
[Middle English fom, from Old English fām.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2019 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.