The Collaborative International Dictionary of English v.0.48:

Deviant \De"vi*ant\, a.
   1. Deviating. [Obs.]
      [1913 Webster]

   2. having behavior or characteristics differing from that
      which is normal or expected, especially in an undesirable
      or socially disapproved manner; as, deviant behavior.

   Syn: deviate. [PJC]

WordNet (r) 3.0 (2006):

deviant
    adj 1: markedly different from an accepted norm; "aberrant
           behavior"; "deviant ideas" [syn: aberrant, deviant,
           deviate]
    n 1: a person whose behavior deviates from what is acceptable
         especially in sexual behavior [syn: pervert, deviant,
         deviate, degenerate]

Moby Thesaurus II by Grady Ward, 1.0:

24 Moby Thesaurus words for "deviant":
   aberrant, abnormal, bent, bizarre, curious, deviate, deviating,
   different, divergent, eccentric, freaky, homosexual, idiosyncratic,
   kinky, odd, offbeat, peculiar, queer, quirky, singular, strange,
   uncommon, unusual, weird