WordNet (r) 3.0 (2006):

incommunicado
    adj 1: without the means or right to communicate; "a prisoner
           held incommunicado"; "incommunicado political detainees"

Moby Thesaurus II by Grady Ward, 1.0:

35 Moby Thesaurus words for "incommunicado":
   abstruse, beclouded, blind, buried, close, clouded, concealed,
   covered, covert, eclipsed, hid, hidden, in a cloud, in a fog,
   in eclipse, in purdah, in the wings, latent, mysterious,
   obfuscated, obscure, obscured, occult, recondite, secluded,
   secluse, secret, sequestered, under an eclipse, under cover,
   under house arrest, under wraps, underground, unknown,
   wrapped in clouds