planet gear vs epicyclic gear

planet gear and epicyclic gear both are nouns.

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

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

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

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

planet gear (noun)	epicyclic 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