The Collaborative International Dictionary of English v.0.48:

Uncommunicative \Uncommunicative\
   See communicative.

WordNet (r) 3.0 (2006):

uncommunicative
    adj 1: not inclined to talk or give information or express
           opinions [syn: uncommunicative, incommunicative]
           [ant: communicative, communicatory]

Moby Thesaurus II by Grady Ward, 1.0:

72 Moby Thesaurus words for "uncommunicative":
   aloof, autistic, bashful, canny, careful, cautious, circumspect,
   close, close-lipped, close-tongued, closemouthed, dark, deliberate,
   discreet, disinclined to communicate, dissociable, distant,
   evasive, gingerly, guarded, heedful, hesitant, incompatible,
   insociable, judicious, leaving out nothing, meaningless, mindful,
   mopey, mopish, morose, noncommittal, nongregarious, offish,
   on guard, overlooking no possibility, pawky, politic, prudent,
   regardful, reserved, reticent, safe, secret, secretive,
   self-contained, self-sufficient, shifty, slow to act, snug,
   socially incompatible, standoffish, sullen, taciturn, tentative,
   thorough, tight-lipped, unadventurous, unapproachable, unbending,
   unclubbable, uncompanionable, uncongenial, unconversable, undaring,
   unenterprising, unfriendly, ungenial, unprecipitate, unsociable,
   unsocial, withdrawn