foam / fōm/ • n. a mass of small bubbles formed on or in liquid, typically by agitation or fermentation: a beer with a thick head of foam. ∎  a similar mass formed from saliva or sweat. ∎  a thick preparation containing many small bubbles: shaving cream (foam type) does a fine job on my beard. ∎  a lightweight form of rubber or plastic made by solidifying such a liquid. ∎  (the foam) poetic/lit. the sea: Venus rising from the foam.• v. [intr.] form or produce a mass of small bubbles; froth: the sea foamed beneath them. ∎ fig., inf. be very angry: the audience was foaming at the mouth, venting their outrage.DERIVATIVES: foam·less adj.foam·y adj.

foam sb. OE. fām = (O)HG. feim :- WGmc. faima :- IE. *poimo-, rel. to L. pūmex PUMICE, OSl. pěna, Skr. phéna- foam.
Hence vb. XIV.