The Collaborative International Dictionary of English v.0.48:

blowjob \blow"job`\, blow job \blow" job`\n.
   An act of fellatio, a form of oral sex; -- a slang term.
   See blow[11], v. i. [Vulgar slang]

   Syn: cock sucking.
        [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

blowjob
    n 1: slang for fellatio [syn: cock sucking, blowjob]