WordNet (r) 3.0 (2006):

leery
    adj 1: openly distrustful and unwilling to confide [syn:
           leery, mistrustful, suspicious, untrusting,
           wary]

Moby Thesaurus II by Grady Ward, 1.0:

37 Moby Thesaurus words for "leery":
   Pyrrhonic, agnostic, cagey, careful, cautious, chary,
   disinclined to believe, disposed to doubt, distrustful, doubtful,
   doubting, dubious, from Missouri, guarded, hard of belief,
   impervious to persuasion, in doubt, inconvincible, incredulous,
   mistrustful, mistrusting, questioning, sceptical, scrupulous, shy,
   shy of belief, skeptical, suspecting, suspicious, uncertain,
   unconvincible, uncredulous, unpersuadable, unpersuasible,
   untrusting, unwilling to accept, wary