Source : Webster's Revised Unabridged Dictionary (1913)

Treadwheel \Tread"wheel`\, n.
   A wheel turned by persons or animals, by treading, climbing,
   or pushing with the feet, upon its periphery or face. See
   {Treadmill}.

Source : WordNet®

treadwheel
     n : a mill that is powered by men or animals walking on a
         circular belt or climbing steps [syn: {treadmill}, {tread-wheel}]