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.