The Collaborative International Dictionary of English v.0.48:

Imprison \Im*pris"on\, v. t. [imp. & p. p. Imprisoned; p. pr.
   & vb. n. Imprisoning.] [OE. enprisonen, OF. enprisoner, F.
   emprisonner; pref. en- (L. in) + F. & OF. prison. See
   Prison.]
   1. To put in prison or jail; To arrest and detain in custody;
      to confine.
      [1913 Webster]

            He imprisoned was in chains remediless. --Spenser.
      [1913 Webster]

   2. To limit, restrain, or confine in any way.
      [1913 Webster]

            Try to imprison the resistless wind.  --Dryden.

   Syn: To incarcerate; confine; immure.
        [1913 Webster]

WordNet (r) 3.0 (2006):

imprisoned
    adj 1: being in captivity [syn: captive, confined,
           imprisoned, jailed]

Moby Thesaurus II by Grady Ward, 1.0:

41 Moby Thesaurus words for "imprisoned":
   barred, behind bars, beleaguered, beset, besieged, blockaded,
   bound, cabined, caged, cloistered, closed-in, confined, cooped,
   cordoned, cordoned off, corralled, cramped, cribbed, enclosed,
   fenced, hedged, hemmed, immured, in captivity, in durance vile,
   in prison, in stir, incarcerated, jailed, leaguered, locked up,
   mewed, paled, penned, pent-up, quarantined, railed, restrained,
   shut-in, walled, walled-in