Definition of comet in US English:



  • A celestial object consisting of a nucleus of ice and dust and, when near the sun, a “tail” of gas and dust particles pointing away from the sun.

    Originating in the remotest regions of the solar system, most comets follow regular eccentric orbits and appear in the inner solar system as periodic comets, some of which break up and can be the origin of annual meteor showers. They were formerly considered to be supernatural omens

    • ‘Several bright comets streaked across the sky and then disappeared in an instant.’
    • ‘The spacecraft will orbit the comet's nucleus.’
    • ‘As orbiting comets pass near the sun, intense heat strips them of a layer of dust and ice.’
    • ‘A bright comet had appeared on 14 November 1680.’
    • ‘Some explanations for extinctions and evolution include strikes by asteroids or comets.’
    • ‘In particular he showed that comets have a solid nucleus, and that they generate their own light.’
    • ‘Bombardment by asteroids and comets is an extraterrestrial process that may release huge quantities of water.’
    • ‘Dozens of comets are discovered each year as well, many by automated telescopes and spacecraft.’
    • ‘Sometimes, the stresses are strong enough to break off chunks of the comet's nucleus.’
    • ‘He observed the comets of 1665, and made other astronomical observations, publishing his descriptions of these events.’
    • ‘The Hawaii researchers observed the comet on July 17 and July 18 and discovered many more fragments.’
    • ‘She discovered eight comets, a record by a female astronomer until 1987.’
    • ‘Rather, they are produced by bits of dusty debris shed by orbiting comets and asteroids.’
    • ‘A bright comet is a spectacular astronomical event.’
    • ‘Warming from the sun causes frozen organic compounds on a comet's surface to sublime, or vaporize.’
    • ‘There are vast numbers of comets in the solar system, more than there are asteroids, but most lie out of sight beyond Pluto.’
    • ‘The spacecraft's point of view now captures the shadowed side of the comet's nucleus.’
    • ‘He saw a comet passing far, far away in the distance from where he made his steps.’
    • ‘A comet is discovered and as it comes closer to earth, it becomes apparent it may strike our planet.’
    • ‘We have just discussed some of the positive benefits of planetary impact by comets and asteroids.’


Late Old English, from Latin cometa, from Greek komētēs ‘long-haired (star)’, from komē ‘hair’; reinforced by Old French comete.