epicyclic gear vs gear wheel

epicyclic gear and gear wheel both are nouns.

Word	Noun	Adjective	Verb	Adverb
epicyclic gear	Yes	No	No	No
gear wheel	Yes	No	No	No

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

epicyclic gear: an outer gear that revolves about a central sun gear of an epicyclic train
gear wheel: a toothed wheel that engages another toothed mechanism in order to change the speed or direction of transmitted motion

Other hypernyms of epicyclic gear include cogwheel, gear, geared wheel.

epicyclic gear (noun)	gear wheel (noun)
an outer gear that revolves about a central sun gear of an epicyclic train	a toothed wheel that engages another toothed mechanism in order to change the speed or direction of transmitted motion