From WordNet (r) 3.0 (2006):
froth
n 1: a mass of small bubbles formed in or on a liquid; "the beer
had a thick head of foam" [syn: foam, froth]
v 1: become bubbly or frothy or foaming; "The boiling soup was
frothing"; "The river was foaming"; "Sparkling water" [syn:
foam, froth, fizz, effervesce, sparkle, form
bubbles]
2: make froth or foam and become bubbly; "The river foamed"
[syn: froth, spume, suds]
3: exude or expel foam; "the angry man was frothing at the
mouth"