The Collaborative International Dictionary of English v.0.48:

ill-gotten \ill-gotten\ adj.
   obtained illegally or by improper means; as, ill-gotten
   gains.

   Syn: dirty.
        [WordNet 1.5] ill-humored

WordNet (r) 3.0 (2006):

ill-gotten
    adj 1: obtained illegally or by improper means; "dirty money";
           "ill-gotten gains" [syn: dirty, ill-gotten]

Moby Thesaurus II by Grady Ward, 1.0:

55 Moby Thesaurus words for "ill-gotten":
   amoral, conscienceless, corrupt, corrupted, criminal, crooked,
   dark, devious, dishonest, dishonorable, doubtful, dubious, evasive,
   evil-eyed, evil-faced, evil-fashioned, evil-favored, evil-gotten,
   evil-looking, evil-minded, felonious, fishy, fraudulent,
   ill-affected, ill-conceived, ill-fashioned, ill-favored, ill-got,
   ill-looking, ill-shaped, immoral, indirect, insidious, not kosher,
   questionable, rotten, shady, shameless, shifty, sinister, slippery,
   suspicious, tricky, unconscienced, unconscientious, unconscionable,
   underhand, underhanded, unethical, unprincipled, unsavory,
   unscrupulous, unstraightforward, without remorse, without shame