Foam v. i. [imp. & p. p. Foamed p. pr. & vb. n. Foaming.]
  1. To gather foam; to froth; as, the billows foam.
     He foameth, and gnasheth with his teeth.   --Mark ix. 18.
  2. To form foam, or become filled with foam; -- said of a steam boiler when the water is unduly agitated and frothy, as because of chemical action.