The Collaborative International Dictionary of English v.0.48:

Unsuccessful \Un`suc*cess"ful\, a.
   Not successful; not producing the desired event; not
   fortunate; meeting with, or resulting in, failure; unlucky;
   unhappy. -- Un`suc*cess"ful*ly, adv. --
   Un`suc*cess"ful*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

unsuccessful
    adj 1: not successful; having failed or having an unfavorable
           outcome [ant: successful]
    2: failing to accomplish an intended result; "an abortive
       revolt"; "a stillborn plot to assassinate the President"
       [syn: abortive, stillborn, unsuccessful]

Moby Thesaurus II by Grady Ward, 1.0:

24 Moby Thesaurus words for "unsuccessful":
   abortive, balked, beaten, bootless, cursed, defeated, foiled,
   fruitless, frustrated, hapless, ineffective, ineffectual,
   inefficacious, luckless, sterile, unavailing, unfortunate,
   unfruitful, unlucky, unproductive, unprofitable, useless, vain,
   worthless