'Planet gear' definitions:

Definition of 'planet gear'

noun

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

From: GCIDE

Planet \Plan"et\, n. [OE. planete, F. plan[`e]te, L. planeta, fr. Gr. ?, and ? a planet; prop. wandering, fr. ? to wander, fr. ? a wandering.]
1. (Astron.) A celestial body which revolves about the sun in an orbit of a moderate degree of eccentricity. It is distinguished from a comet by the absence of a coma, and by having a less eccentric orbit. See Solar system. [1913 Webster]
Note: The term planet was first used to distinguish those stars which have an apparent motion through the constellations from the fixed stars, which retain their relative places unchanged. The inferior planets are Mercury and Venus, which are nearer to the sun than is the earth; the superior planets are Mars, the asteroids, Jupiter, Saturn, Uranus, and Neptune, which are farther from the sun than is the earth. Primary planets are those which revolve about the sun; secondary planets, or moons, are those which revolve around the primary planets as satellites, and at the same time revolve with them about the sun. [1913 Webster]
2. A star, as influencing the fate of a men. [1913 Webster]
There's some ill planet reigns. --Shak. [1913 Webster]
Planet gear. (Mach.) See Epicyclic train, under Epicyclic.
Planet wheel, a gear wheel which revolves around the wheel with which it meshes, in an epicyclic train. [1913 Webster]