Merriam-Webster Collegiate Dictionary - foam

 I. noun  Etymology: Middle English fome, from Old English fam; akin to Old High German feim ~, Latin spuma ~, pumex pumice  Date: before 12th century  1. a light frothy mass of fine bubbles formed in or on the surface of a liquid or from a liquid: as  a. a frothy mass formed in salivating or sweating  b. a stabilized froth produced chemically or mechanically and used especially in fighting oil fires  c. a material in a lightweight cellular form resulting from introduction of gas bubbles during manufacture  2. sea  3. something resembling ~  • ~less adjective  II. verb  Date: before 12th century  intransitive verb  1.  a. to produce or form ~  b. to froth at the mouth especially in anger; broadly to be angry  2. to gush out in ~  3. to become covered with or as if with ~ streets…~ing with life — Thomas Wolfe  transitive verb  1. to cause to ~; specifically to cause air bubbles to form in  2. to convert (as a plastic) into a ~  • ~able adjective  • ~er noun