tread-wheel vs treadwheel

tread-wheel and treadwheel both are nouns.

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

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

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

Other synonyms of tread-wheel include treadmill.

tread-wheel (noun)	treadwheel (noun)
a mill that is powered by men or animals walking on a circular belt or climbing steps	a mill that is powered by men or animals walking on a circular belt or climbing steps