Merriam-Webster Collegiate Dictionary - turret

 noun  Etymology: Middle English touret, from Anglo-French turette, tourette, diminutive of tur, tour tower — more at tower  Date: 14th century  1. a little tower; specifically an ornamental structure at an angle of a larger structure  2.  a. a pivoted and revolvable holder in a machine tool  b. a device (as on a microscope or a television camera) holding several lenses  3.  a. a tall building usually moved on wheels and formerly used for carrying soldiers and equipment for breaching or scaling a wall  b.  (1) a gunner's fixed or movable enclosure in an airplane  (2) a revolving armored structure on a warship that protects one or more guns mounted within it  (3) a similar upper structure usually for one gun on a tank