The Collaborative International Dictionary of English v.0.48:

Unconventional \Unconventional\
   See conventional.

WordNet (r) 3.0 (2006):

unconventional
    adj 1: not conforming to accepted rules or standards; "her
           unconventional dress and hair style" [ant:
           conventional]
    2: not conventional or conformist; "unconventional life styles"
       [ant: conventional]
    3: not conforming to legality, moral law, or social convention;
       "an unconventional marriage"; "improper banking practices"
       [syn: improper, unconventional, unlawful]

Moby Thesaurus II by Grady Ward, 1.0:

83 Moby Thesaurus words for "unconventional":
   Bohemian, abnormal, affable, anomalous, beat, breakaway, casual,
   cordial, crank, crankish, cranky, crotchety, degage, deviant,
   deviative, different, divergent, dotty, easy, easygoing, eccentric,
   erratic, exceptional, familiar, far out, fey, flaky, folksy,
   freakish, free and easy, fringy, funny, gracious, haymish,
   heretical, heterodox, hippie, homely, homey, idiocratic,
   idiosyncratic, informal, irregular, kinky, kooky, loose, maggoty,
   maverick, natural, not cricket, not done, not kosher, nutty, odd,
   oddball, offbeat, offhand, offhanded, original, peculiar, plain,
   queer, quirky, relaxed, screwball, screwy, simple, singular,
   sociable, strange, twisted, unaffected, unassuming, unceremonious,
   unconstrained, unfashionable, unnatural, unofficial, unorthodox,
   unstudied, wacky, way out, whimsical