planet wheel vs planetary gear

planet wheel and planetary gear both are nouns.

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

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

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

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

planet wheel (noun)	planetary 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