mill wheel vs waterwheel

mill wheel and waterwheel both are nouns.

Word	Noun	Adjective	Verb	Adverb
mill wheel	Yes	No	No	No
waterwheel	Yes	No	No	No

As nouns, waterwheel is a hypernym of mill wheel; that is, waterwheel is a word with a broader meaning than mill wheel:

mill wheel: water wheel that is used to drive machinery in a mill
waterwheel: a wheel that rotates by direct action of water; a simple turbine

Other hypernyms of mill wheel include water wheel.

mill wheel (noun)	waterwheel (noun)
water wheel that is used to drive machinery in a mill	a wheel that rotates by direct action of water; a simple turbine
	a wheel with buckets attached to its rim; raises water from a stream or pond