turret

noun

a small tower projecting from a building, usually at a corner and often merely ornamental
a wooden, usually square tower on wheels, carrying soldiers, battering-rams, catapults, etc., used in ancient warfare for attacking fortresses and walled cities
1. a low, armored, usually revolving, structure for a gun or guns, as on a warship, tank, or fortress
2. a transparent dome for a gun and gunner, as on a bomber
an attachment for a lathe, drill, etc., consisting of a block holding several cutting tools, which may be rotated to present any of the tools to the work
also turrethead
an adjustable device on a camera for holding various lenses

See turret in American Heritage Dictionary 4