Com"et (?), n. [L. cometes, cometa, from Gr. &?; comet, prop. long-haired, fr. &?; to wear long hair, fr. &?; hair, akin to L. coma: cf. F. comète.] (Astron.) A member of the solar system which usually moves in an elongated orbit, approaching very near to the sun in its perihelion, and receding to a very great distance from it at its aphelion. A comet commonly consists of three parts: the nucleus, the envelope, or coma, and the tail; but one or more of these parts is frequently wanting. See Illustration in Appendix.

• A celestial body consisting mainly of ice, dust and gas in a (usually very eccentric) orbit around the Sun and having a "tail" of melted matter blown back from it by the solar wind as it approaches the Sun.