(astronomy, planets) A planet larger than terrestrial planets, composed mostly of gases and astronomical ices.

the planet Earth

(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.

(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.

Synonym of planet-struck

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

(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.

(now chiefly historical) A white witch.

plural of planet-ruler