means A small tower projecting from a building or vehicle, often rounded, that may house a lookout, a staircase, or a rotating gun.

from From Old French 'tourete,' a diminutive of 'tour' meaning tower — literally 'little tower' — which traces back to Latin 'turris,' tower. The word arrived in English in the medieval period, when a turret really was a slender tower clinging to a castle wall. The spinning sense — the rotating gun mount on a ship or tank — is a much later borrowing of the same shape, a little tower that swivels.