late 14c., from L. cælestis "heavenly," from cælum "heaven, sky," of uncertain origin; perhaps from PIE *kaid-slo-, from a root meaning "bright." The L. word is the source of the usual word for "sky" in most of the Romance languages, e.g. French ciel, Sp. cielo, It. cielo.
Relating to the sky or the heavens. Stars and planets are celestial bodies.
Relating to the celestial sphere or to any of the coordinate systems by which the position of an object, such as a star or planet, is represented on it.