(astronomy) a planet that shares similar physical characteristics, such as size, density and mass, with another planet

(archaic, astronomy) A moon of a planet besides Earth; a secondary planet; a natural planetary satellite.

plural of planet gear

(engineering) An epicyclic gear; the middle gears in a planetary gear system, spun by the central sun gear

Synonym of planet-struck

(astronomy, celestial mechanics) An imaginary celestial body (corresponding to another, real, orbiting one) which orbits with constant speed along an auxiliary circle (a circle which shares a diameter with the major axis of the elliptical orbit of the corresponding real celestial body), such that its position coincides with the position of the corresponding, real celestial body when that body passes through periapsis.

A gear wheel that revolves around the wheel with which it meshes, in an epicyclic train.

(archaic) Afflicted by the astrological influence of a planet; struck down with amazement or shock; panic-stricken.

plural of planet-ruler

(astronomy, planetology) a planetary-mass object which has either been ejected from its system or was never gravitationally bound to any star or other such object, and that therefore orbits the galaxy directly.