The Collaborative International Dictionary of English v.0.48:

Billow \Bil"low\, v. i. [imp. & p. p. Billowed; p. pr. & vb.
   n. Billowing.]
   To surge; to rise and roll in waves or surges; to undulate.
   "The billowing snow." --Prior.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

billowing \billowing\ adj. [p. pr. & vb. n. of billow, verb]
   1. rising in billows. billowing smoke
      [WordNet 1.5]

   2. stormy; affected by storms; -- of weather, used
      prenominally. calm

   Syn: billowy, surging.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

billowing
    adj 1: characterized by great swelling waves or surges; "billowy
           storm clouds"; "the restless billowing sea"; "surging
           waves" [syn: billowy, billowing(a), surging]