planet wheel vs planet gear

planet wheel and planet gear both are nouns.

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

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

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

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

planet wheel (noun)	planet gear (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