The Collaborative International Dictionary of English v.0.48:

Throttle \Throt"tle\, n. [Dim. of throat. See Throat.]
   1. The windpipe, or trachea; the weasand. --Sir W. Scott.
      [1913 Webster]

   2. (Steam Engine) The throttle valve.
      [1913 Webster]

   Throttle lever (Steam Engine), the hand lever by which a
      throttle valve is moved, especially in a locomotive.

   Throttle valve (Steam Engine), a valve moved by hand or by
      a governor for regulating the supply of steam to the steam
      chest. In one form it consists of a disk turning on a
      transverse axis.
      [1913 Webster]

WordNet (r) 3.0 (2006):

throttle valve
    n 1: a valve that regulates the supply of fuel to the engine
         [syn: accelerator, throttle, throttle valve]