The Collaborative International Dictionary of English v.0.48:

Turret \Tur"ret\, n. [OE. touret, OF. tourette, dim. of tour a
   tower, L. turris. See Tower.]
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   1. (Arch.) A little tower, frequently a merely ornamental
      structure at one of the angles of a larger structure.
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   2. (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.
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   3. (Mil.) A revolving tower constructed of thick iron plates,
      within which cannon are mounted. Turrets are used on
      vessels of war and on land.
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   4. (Railroads) The elevated central portion of the roof of a
      passenger car. Its sides are pierced for light and
      ventilation.
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   Turret clock, a large clock adapted for an elevated
      position, as in the tower of a church.

   Turret head (Mach.), a vertical cylindrical revolving tool
      holder for bringing different tools into action
      successively in a machine, as in a lathe.

   Turret lathe, a turning lathe having a turret head.

   Turret ship, 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.
      [1913 Webster]

WordNet (r) 3.0 (2006):

turret clock
    n 1: a clock with more than one dial to show the time in all
         directions from a tower