planetary gear vs planet wheel

planetary gear and planet wheel both are nouns.

Word	Noun	Adjective	Verb	Adverb
planetary gear	Yes	No	No	No
planet wheel	Yes	No	No	No

As nouns, planetary gear and planet wheel are synonyms defined as:

planetary gear and planet wheel: an outer gear that revolves about a central sun gear of an epicyclic train

Other synonyms of planetary gear include epicyclic gear, planet gear.

planetary gear (noun)	planet wheel (noun)
an outer gear that revolves about a central sun gear of an epicyclic train	an outer gear that revolves about a central sun gear of an epicyclic train