The Collaborative International Dictionary of English v.0.48:

Foam \Foam\ (f[=o]m), n. [OE. fam, fom, AS. f[=a]m; akin to OHG.
   & G. feim.]
   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; as, the foam of the sea.
   [1913 Webster]

   Foam cock, in steam boilers, a cock at the water level, to
      blow off impurities.
      [1913 Webster]