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Wiktionary
planetary gear

n. an epicyclic gear

WordNet
planetary gear

n. an outer gear that revolves about a central sun gear of an epicyclic train [syn: epicyclic gear, planet wheel, planet gear]

Usage examples of "planetary gear".

Tyrel looks at the swiftly stroking rods, the planetary gear, and the flywheel.

With a slate-pencil screech the driver engaged his planetary gear and they were off.