turret

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A small tower or tower-shaped projection on a building.
• noun A low, heavily armored structure, usually rotating horizontally, containing mounted guns and their gunners or crew, as on a warship or tank.
• noun A domelike gunner's enclosure projecting from the fuselage of a combat aircraft.
• noun A tall wooden structure mounted on wheels and used in ancient warfare by besiegers to scale the walls of an enemy fortress.
• noun An attachment for a lathe consisting of a rotating cylindrical block holding various cutting tools.
• noun A rotating device holding various lenses, as for a microscope, allowing easy switching from one lens to another.

from The Century Dictionary.

• noun An attachment to a lathe, drill, boring-machine, or slotting-machine designed to hold and present to the work a series of boring-, drilling-, or cutting-tools, the object being to save the time lost in changing from one tool to another by hand.
• noun A little tower rising from or otherwise connected with a larger building; a small tower, often crowning or finishing the angle of a wall, etc.
• noun In medieval warfare, a movable building of a square form, consisting of ten or even twenty stories, and sometimes 180 feet high, usually moved on wheels, and employed in approaches to a fortified place for carrying soldiers, engines, ladders, etc.
• noun Milit., a tower, often revolving, for offensive purposes, on land or water. See cut under monitor.
• noun In her.: A small slender tower, usually forming part of a bearing, being set upon a larger tower. Sec turreted, 3.
• noun A bearing representing a kind of scepter having both ends alike and resembling the ends of the cross avellane. See tirret.
• noun In a railroad-car of American model, the raised part of the middle of the roof, utilized for affording light and ventilation.
• noun In a lathe, a cylindrical or polygonal block on the bed, with holes around it for dies.
• noun Same as terret.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Arch.) A little tower, frequently a merely ornamental structure at one of the angles of a larger structure.
• noun (Anc. Mil.) 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.
• noun (Mil.) A revolving tower constructed of thick iron plates, within which cannon are mounted. Turrets are used on vessels of war and on land.
• noun (Railroads) The elevated central portion of the roof of a passenger car. Its sides are pierced for light and ventilation.
• noun a large clock adapted for an elevated position, as in the tower of a church.
• noun (Mach.) a vertical cylindrical revolving tool holder for bringing different tools into action successively in a machine, as in a lathe.
• noun a turning lathe having a turret head.
• noun an ironclad war vessel, with low sides, on which heavy guns are mounted within one or more iron turrets, which may be rotated, so that the guns may be made to bear in any required direction.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun architecture a little tower, frequently a merely ornamental structure at one of the corners of a building or castle
• noun 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
• noun military an armoured, rotating gun installation, on a fort, ship, aircraft, or armoured fighting vehicle
• noun rail transport the elevated central portion of the roof of a passenger car. Its sides are pierced for light and ventilation
• noun electronics a tower-like solder post on a turret board (a circuit board with posts instead of holes)

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a self-contained weapons platform housing guns and capable of rotation
• noun a small tower extending above a building