n. In fortification: A vault of stone or brickwork, usually built in the thickness of the rampart of a fortress, and pierced in front with embrasures, through which artillery may be fired.n. A shell-proof vault of stone or brick designed to protect troops, ammunition, etc.n. An embrasure.n. The armored bulkhead surrounding guns in iron-clad ships of war, and pierced with portholes through which the guns are run out.n. An erroneous form of casement, .