WordNet (r) 3.0 (2006):

dud
    adj 1: failing to detonate; especially not charged with an
           active explosive; "he stepped on a dud mine"
    n 1: someone who is unsuccessful [syn: flop, dud, washout]
    2: an explosion that fails to occur [syn: misfire, dud]
    3: an event that fails badly or is totally ineffectual; "the
       first experiment was a real turkey"; "the meeting was a dud
       as far as new business was concerned" [syn: turkey, bomb,
       dud]

Moby Thesaurus II by Grady Ward, 1.0:

60 Moby Thesaurus words for "dud":
   abortion, abortive attempt, also-ran, aspirant, baby kisser,
   bankrupt, blank cartridge, bogy, bomb, bugaboo, bugbear, bust,
   candidate, castrato, cipher, cry of wolf, dark horse,
   defeated candidate, dummy, eunuch, failure, false alarm,
   favorite son, flop, gelding, hollow man, hopeful, impotent,
   incompetent, invalid, jackstraw, lame duck, lay figure, lemon,
   loser, man of straw, merry chase, miscarriage, miscarrying,
   misfire, nebbish, nobody, nonentity, nothing, nullity,
   office seeker, political hopeful, presidential timber, puppet,
   pushover, running mate, stalking-horse, thing of naught, trifle,
   vain attempt, washout, weakling, wet squib, wild-goose chase,
   zero