The Collaborative International Dictionary of English v.0.48:

standoffish \stand*off"ish\, stand-offish \stand-off"ish\a.
   Shy or distant in manner; cold; aloof; reserved; not
   friendly.

   Syn: offish.
        [PJC] -- stand*off"ish*ness, n. -- stand*off"ish*ly,
        adv.
        [PJC]

WordNet (r) 3.0 (2006):

standoffish
    adj 1: lacking cordiality; unfriendly; "a standoffish manner"
           [syn: offish, standoffish]

Moby Thesaurus II by Grady Ward, 1.0:

60 Moby Thesaurus words for "standoffish":
   Olympian, above all that, aloof, backward, bashful, blank, chilled,
   chilly, cold, constrained, cool, detached, discreet, distant,
   eremitic, exclusive, expressionless, forbidding, frigid, frosty,
   guarded, haughty, highfalutin, icy, impassive, impersonal,
   inaccessible, insociable, introverted, lordly, misanthropic,
   modest, offish, pompous, reclusive, remote, removed, repressed,
   reserved, restrained, reticent, retiring, seclusive, shrinking,
   snooty, solitary, standoff, subdued, suppressed, unaffable,
   unapproachable, uncompanionable, uncongenial, undemonstrative,
   unexpansive, unfriendly, ungenial, unsociable, unsocial,
   withdrawn