The Collaborative International Dictionary of English v.0.48:

Hostage \Hos"tage\, n. [OE. hostage, OF. hostage, ostage, F.
   [^o]tage, LL. hostaticus, ostaticum, for hospitaticum, fr. L.
   hospes guest, host. The first meaning is, the state of a
   guest, hospitality; hence, the state of a hostage (treated as
   a guest); and both these meanings occur in Old French. See
   Host a landlord.]
   A person given as a pledge or security for the performance of
   the conditions of a treaty or stipulations of any kind, on
   the performance of which the person is to be released.
   [1913 Webster]

         Your hostages I have, so have you mine;
         And we shall talk before we fight.       --Shak.
   [1913 Webster]

         He that hath a wife and children hath given hostages to
         fortune.                                 --Bacon.
   [1913 Webster]

WordNet (r) 3.0 (2006):

hostage
    n 1: a prisoner who is held by one party to insure that another
         party will meet specified terms [syn: hostage, surety]

Moby Thesaurus II by Grady Ward, 1.0:

25 Moby Thesaurus words for "hostage":
   bail, bond, captive, earnest, earnest money, escrow, gage,
   guaranty, handsel, hock, mainprise, pawn, pignus, pledge, prisoner,
   recognizance, replevin, replevy, security, surety, token,
   token payment, undertaking, vadimonium, vadium



Easton's 1897 Bible Dictionary:

Hostage
   a person delivered into the hands of another as a security for
   the performance of some promise, etc. (2 Kings 14:14; 2 Chr.
   25:24).