turret

(architecture) A little tower, frequently a merely ornamental structure at one of the corners of a building or castle.

(historical, military) A siege tower; a movable building, of a square form, consisting of ten or even twenty stories and sometimes one hundred and twenty cubits high, usually moved on wheels, and employed in approaching a fortified place, for carrying soldiers, engines, ladders, casting bridges, and other necessaries.

(electronics) A tower-like solder post on a turret board (a circuit board with posts instead of holes).

(military) An armoured, rotating gun installation on a fort, ship, aircraft, or armoured fighting vehicle.

(rail transport) The elevated central portion of the roof of a passenger car, with sides that are pierced for light and ventilation.