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]