: a celestial body that appears as a fuzzy head usually surrounding a bright nucleus, that has a usually highly eccentric orbit, that consists primarily of ice and dust, and that often develops one or more long tails when near the sun
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Research teams can propose their concepts for a new space telescope or a probe to a comet or an asteroid, for example, when NASA puts out a call for proposals.
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Stephen Clark, ArsTechnica, 19 May 2026
The space rock was first spotted on May 10 by astronomers at Tucson’s Mount Lemmon Survey, the same observatory that discovered a spectacular comet visible with the naked eye last year.
—Adam Kovac, Scientific American, 18 May 2026
Astronomers routinely track asteroids and comets that could come near Earth using a network of telescopes on the ground and in space.
—Denise Chow, NBC news, 18 May 2026
Scientists announced the observation of an interstellar comet called 3I/ATLAS on July 1, 2025.
—Quanta Magazine, 15 May 2026
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Stephen Clark, ArsTechnica, 19 May 2026
The space rock was first spotted on May 10 by astronomers at Tucson’s Mount Lemmon Survey, the same observatory that discovered a spectacular comet visible with the naked eye last year.
—Adam Kovac, Scientific American, 18 May 2026
Astronomers routinely track asteroids and comets that could come near Earth using a network of telescopes on the ground and in space.
—Denise Chow, NBC news, 18 May 2026
Scientists announced the observation of an interstellar comet called 3I/ATLAS on July 1, 2025.
—Quanta Magazine, 15 May 2026
See All Example Sentences for comet
Cite this Entry
“Comet.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/comet. Accessed 21 May. 2026.
Copy CitationKids Definition
comet
noun
com·et
ˈkäm-ət 
: a bright heavenly body that develops a cloudy tail as it moves closer to the sun in its orbit
Etymology
Old English cometa "comet," from Latin cometa (same meaning), from Greek komētēs, literally, "long-haired," derived from komē "hair" — related to coma entry 2
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