fortress

from WordNet (r) 3.0 (2006)

fortress
    n 1: a fortified defensive structure [syn: {fortress}, {fort}]

from The Collaborative International Dictionary of English v.0.48

Fortress \For"tress\, v. t.
   To furnish with a fortress or with fortresses; to guard; to
   fortify. --Shak.
   [1913 Webster]

from The Collaborative International Dictionary of English v.0.48

Fortress \For"tress\, n.; pl. {Fortresses}. [F. forteresse, OF.
   forteresce, fortelesce, LL. foralitia, fr. L. fortis strong.
   See {Fort}, and cf. {Fortalice}.]
   A fortified place; a large and permanent fortification,
   sometimes including a town; a fort; a castle; a stronghold; a
   place of defense or security.

   Syn: {Fortress}, {Fortification}, {Castle}, {Citadel}.

   Usage: A fortress is constructed for military purposes only,
          and is permanently garrisoned; a fortification is
          built to defend harbors, cities, etc.; a castle is a
          fortress of early times which was ordinarily a
          palatial dwelling; a citadel is the stronghold of a
          fortress or city, etc.
          [1913 Webster]

from Moby Thesaurus II by Grady Ward, 1.0

32 Moby Thesaurus words for "fortress":
      acropolis, bastion, beachhead, blockhouse, bridgehead, bunker,
      castle, citadel, donjon, fasthold, fastness, fort, garrison,
      garrison house, hold, keep, martello, martello tower, mote, motte,
      peel, peel tower, pillbox, post, rath, redoubt, safehold,
      strong point, stronghold, tower, tower of strength, ward