The Collaborative International Dictionary of English v.0.48:
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. [1913 Webster]WordNet (r) 3.0 (2006):
treadwheel n 1: a mill that is powered by men or animals walking on a circular belt or climbing steps [syn: treadmill, treadwheel, tread-wheel]