tread-wheel vs treadmill

tread-wheel and treadmill both are nouns.

Word	Noun	Adjective	Verb	Adverb
tread-wheel	Yes	No	No	No
treadmill	Yes	No	No	No

As nouns, tread-wheel and treadmill are synonyms defined as:

tread-wheel and treadmill: a mill that is powered by men or animals walking on a circular belt or climbing steps

Other synonyms of tread-wheel include treadwheel.

tread-wheel (noun)	treadmill (noun)
a mill that is powered by men or animals walking on a circular belt or climbing steps	a job involving drudgery and confinement
	a mill that is powered by men or animals walking on a circular belt or climbing steps
	an exercise device consisting of an endless belt on which a person can walk or jog without changing place