The Collaborative International Dictionary of English v.0.48:

Turnkey \Turn"key`\ (t[^u]rn"k[=e]`), n.; pl. Turnkeys
   (t[^u]r"k[=e]z`).
   1. A person who has charge of the keys of a prison, for
      opening and fastening the doors; a warder.
      [1913 Webster]

   2. (Dentistry) An instrument with a hinged claw, -- used for
      extracting teeth with a twist.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

turnkey \turn"key`\ (t[^u]rn"k[=e]`), a.
   Of or pertaining to a building, complex device, system, or
   industrial installation which is sold by a contractor only
   after it is ready for immediate occupation or use; fully
   functional and ready for use; -- used of complex systems of a
   type which often require preparation or installation by the
   user before being capable of functioning as intended; as, a
   turnkey ethylene production plant; a turnkey apartment
   building.
   [PJC]

WordNet (r) 3.0 (2006):

turnkey
    n 1: someone who guards prisoners [syn: prison guard,
         jailer, jailor, gaoler, screw, turnkey]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

TURNKEY. A person under the superintendence of a jailor, whose employment is
to open and fasten the prison doors and to prevent the prisoners from
escaping.
     2. It is his duty to use due diligence, and he may be punished for
gross neglect or willful misconduct in permitting prisoners to escape.