A celestial body, observed only in that part of its orbit that is relatively close to the sun, having a head consisting of a solid nucleus surrounded by a nebulous coma up to 2.4 million kilometers (1.5 million miles) in diameter and an elongated curved vapor tail arising from the coma when sufficiently close to the sun. Comets are thought to consist chiefly of ammonia, methane, carbon dioxide, and water.
ETYMOLOGY:
Middle English comete, from Old English comta, from Late Latin, from Latin comts, from Greek komts, long-haired (star), comet, from kom, hair.
OTHER FORMS:
comet·ary (--tr) , co·metic (k-mtk) —ADJECTIVE
WORD HISTORY:
Comets have been feared throughout much of human history, and even in our own time their goings and comings receive great attention. Perhaps a comet might seem less awesome if we realized that our name for it is based on a figurative resemblance between it and humans. This figurative name is recorded first in the works of Aristotle, in which he uses kom, the Greek word for “hair of the head,” to mean “luminous tail of a comet.” Aristotle then uses the derived word komts, “wearing long hair,” as a noun meaning “comet.” The Greek word was adopted into Latin as comts, which was refashioned in Late Latin and given the form comta, furnishing Old English with comta, the earliest English ancestor of our word comet.
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