The Collaborative International Dictionary of English v.0.48:

Seamy \Seam"y\, a.
   Having a seam; containing seams, or showing them. "Many a
   seamy scar." --Burns.
   [1913 Webster]

         Everything has its fair, as well as its seamy, side.
                                                  --Sir W.
                                                  Scott.
   [1913 Webster]

WordNet (r) 3.0 (2006):

seamy
    adj 1: showing a seam
    2: morally degraded; "a seedy district"; "the seamy side of
       life"; "sleazy characters hanging around casinos"; "sleazy
       storefronts with...dirt on the walls"- Seattle Weekly; "the
       sordid details of his orgies stank under his very nostrils"-
       James Joyce; "the squalid atmosphere of intrigue and
       betrayal" [syn: seamy, seedy, sleazy, sordid,
       squalid]

Moby Thesaurus II by Grady Ward, 1.0:

37 Moby Thesaurus words for "seamy":
   abhorrent, contemptible, dark, degenerate, degraded, depraved,
   derogatory, discreditable, dishonorable, disreputable, distasteful,
   foul, ignoble, ignominious, infamous, inglorious, low, nasty,
   notorious, odious, repellent, repulsive, rotten, scurvy, shady,
   shameful, sordid, squalid, ugly, unattractive, unpalatable,
   unpraiseworthy, unrespectable, unsavory, unseemly, unwholesome,
   vile