ntreadwheela mill that is powered by men or animals walking on a circular belt or climbing steps
Webster's Revised Unabridged Dictionary
nTreadwheelA wheel turned by persons or animals, by treading, climbing, or pushing with the feet, upon its periphery or face. See Treadmill.
Century Dictionary and Cyclopedia
ntreadwheelA contrivance for utilizing the weight of men or animals to produce rotary motion, which can then be applied to various mechanical purposes. It is of two principal forms: A hollow cylinder set with the axis horizontal. An animal, as a dog, walks on the inner surface of the cylinder, to which battens are secured as a foothold, and thus revolves it.
Sometimes the savages seemed to enjoy the fun of climbing on the great creaking treadwheel, as though it were a game.