Comet
Webster's Dictionary [1]
(n.) 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.
The Nuttall Encyclopedia [2]
A member of the solar system under control of the sun, consisting of a bright nucleus within a nebulous envelope, generally extended into a tail on the rear of its orbit, which is extremely eccentric, pursuing its course with a velocity which increases as it approaches the sun, and which diminishes as it withdraws from it; these bodies are very numerous, have their respective periods of revolution, which have been in many cases determined by observation.
