Comet \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. com[`e]te.]

(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.

Source: Webster's Revised Unabridged Dictionary (1913)