[1] : The Collaborative International Dictionary of English v.0.48

mutt \mutt\ n.
   an dog that is of inferior quality or of mixed breed.

   syn: cur, mongrel.
        wordnet 1.5

[2] : WordNet (r) 2.0

mutt
     n : an inferior dog or one of mixed breed syn: cur, mongrel
see also:
cur mongrel 

[3] : Moby Thesaurus II by Grady Ward, 1.0

29 moby thesaurus words for "mutt":
   asshole, blockhead, boob, booby, chump, cur, dimwit, ding-a-ling,
   dingbat, dingdong, dolt, dope, dumbbell, galoot, goof, idiot,
   ignoramus, jerk, jerk-off, klutz, lurcher, mongrel, numskull,
   pariah dog, prize sap, sap, saphead, sawney, schlemiel

Mutt >> M Words
Mutt, definition of term: Mutt
mutt_pag1.html