Fortress

Part of speech: noun (n.)

A fortified place; a large and permanent fortification, sometimes including a town; a fort; a castle; a stronghold; a place of defense or security.

Synonyms: 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.

Part of speech: verb (v.)

To furnish with a fortress or with fortresses; to guard; to fortify. Shak.