Fortress (?), 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. 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]