The Collaborative International Dictionary of English v.0.48:

Prisoner \Pris"on*er\, n. [F. prisonnier.]
   1. One who is confined in a prison. --Piers Plowman.
      [1913 Webster]

   2. A person under arrest, or in custody, whether in prison or
      not; a person held in involuntary restraint; a captive;
      as, a prisoner at the bar of a court. --Bouvier.
      [1913 Webster]

            Prisoner of Hope thou art, -- look up and sing.
                                                  --Keble.
      [1913 Webster]

   Prisoner's base. See Base, n., 24.
      [1913 Webster]

WordNet (r) 3.0 (2006):

prisoner
    n 1: a person who is confined; especially a prisoner of war
         [syn: prisoner, captive]

Moby Thesaurus II by Grady Ward, 1.0:

27 Moby Thesaurus words for "prisoner":
   POW, accused, cageling, captive, chain gang, con, convict,
   correspondent, defendant, detainee, detenu, ex-convict, gaolbird,
   internee, jailbird, libelee, lifer, parolee, political prisoner,
   prisoner of war, respondent, stir bird, suspect,
   ticket-of-leave man, ticket-of-leaver, trusty, two-time loser