The Collaborative International Dictionary of English v.0.48:

Turnstile \Turn"stile`\, n.
   1. A revolving frame in a footpath, preventing the passage of
      horses or cattle, but admitting that of persons; a
      turnpike. See Turnpike, n., 1.
      [1913 Webster]

   2. A similar arrangement for registering the number of
      persons passing through a gateway, doorway, or the like.
      [1913 Webster]

WordNet (r) 3.0 (2006):

turnstile
    n 1: a gate consisting of a post that acts as a pivot for
         rotating arms; set in a passageway for controlling the
         persons entering