The Collaborative International Dictionary of English v.0.48:

Incommunicative \In`com*mu"ni*ca*tive\, a.
   Not communicative; not free or apt to impart to others in
   conversation; reserved; silent; as, the messenger was
   incommunicative; hence, not disposed to hold fellowship or
   intercourse with others; exclusive.
   [1913 Webster]

         The Chinese . . . an incommunicative nation. --C.
                                                  Buchanan.
   -- In`com*mu"ni*ca*tive*ly, adv. --
   In`com*mu"ni*ca*tive*ness, n. --Lamb.
   [1913 Webster]

         His usual incommunicativeness.           --G. Eliot.
   [1913 Webster]

WordNet (r) 3.0 (2006):

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