The Collaborative International Dictionary of English v.0.48:

blowhard \blow"hard\ n.
   a very boastful and talkative person.

   Syn: braggart, boaster, line-shooter, vaunter.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

blowhard
    n 1: a very boastful and talkative person [syn: bragger,
         braggart, boaster, blowhard, line-shooter,
         vaunter]