[1] : 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

[2] : 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
see also:
fortresses fort fortalice fortress fortification castle 
citadel 

[3] : WordNet (r) 2.0

fortress
     n : a fortified defensive structure syn: fort
see also:
fort 

[4] : 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

Fortress >> F Words
Fortress, definition of term: Fortress
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