Source : Webster's Revised Unabridged Dictionary (1913)

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.