comet

American  

[kom-it] / ˈkɒm ɪt /

noun

Astronomy.

• comets
  plural

1. a celestial body moving about the sun, usually in a highly eccentric orbit, consisting of a central mass surrounded by an envelope of dust and gas that may form a tail that streams away from the sun.

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comet British  

/ ˈkɒmɪt /

noun

1. a celestial body that travels around the sun, usually in a highly elliptical orbit: thought to consist of a solid frozen nucleus part of which vaporizes on approaching the sun to form a gaseous luminous coma and a long luminous tail

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comet Scientific  

/ kŏm′ĭt /

1. A celestial object that orbits the Sun along an elongated path. A comet that is not near the Sun consists only of a nucleus—a solid core of frozen water, frozen gases, and dust. When a comet comes close to the Sun, its nucleus heats up and releases a gaseous coma that surrounds the nucleus. A comet forms a tail when solar heat or wind forces dust or gas off its coma, with the tail always streaming away from the Sun.

2. ◆ Short-period comets have orbital periods of less than 200 years and come from the region known as the Kuiper belt. Long-period comets have periods greater than 200 years and come from the Oort cloud.

3. See more at Kuiper belt Oort cloud See Note at solar system

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comet Cultural  

1. An object that enters the inner solar system, typically in a very elongated orbit around the sun. Material is boiled off from the comet by the heat of the sun, so that a characteristic tail is formed. The path of a comet can be in the form of an ellipse or a hyperbola. If it follows a hyperbolic path, it enters the solar system once and then leaves forever. If its path is an ellipse, it stays in orbit around the sun.

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Discover More

Comets were once believed to be omens, and their appearances in the sky were greatly feared or welcomed.

The most famous comet, Comet Halley (or Halley's comet), passes close to the Earth roughly every seventy-six years, most recently in 1986.

Other Word Forms

Derived Forms

• cometary
  adjective
• cometic
  adjective
• cometical
  adjective
• cometlike
  adjective

Inflected Forms

Nouns

• comets
  plural

Etymology

Origin of comet

1150–1200; Middle English comete < Anglo-French, Old French < Latin comētēs, comēta < Greek komḗtēs wearing long hair, equivalent to komē-, variant stem of komân to let one's hair grow (derivative of kómē hair) + -tēs agent suffix

Explanation

A comet is a small, icy object that orbits the sun and has a long "tail" of gas. Some comets can be seen from Earth every few years, while others pass by once in a person's lifetime. Comets are made of ice, dust, and tiny pieces of rock, but to people on Earth, they look like streaks or smudges across the night sky. When the Earth's orbit takes it through one of these comets' tails, their dust burns up in our atmosphere and results in a meteor shower. In Old French, the word was comete, ultimately from a Greek root, kometes, which literally means "long-haired star."

Example Sentences

See Examples For:

comet comets

Conversation in the house during these years often focused on global catastrophic risks ranging from comet strikes to supervolcanoes, according to a person who spent time there.

From The Wall Street Journal ● Sep. 27, 2026

It’s a dizzying thought, the comet from Norristown sharing space with Man City stars like the Norwegian Thunder God Erling Haaland.

From The Wall Street Journal ● Sep. 24, 2026

The Perseids, pronounced 'Per-see-ids', are caused by debris left behind specifically by the Swift-Tuttle comet.

From BBC ● Aug. 11, 2026

The comet was exceptionally difficult to detect with these instruments.

From Science Daily ● Jul. 24, 2026

Just before Jason blacked out, the comet intercepted the ball of fire above them.

From "Blood of Olympus" by Rick Riordan

In fact, its methanol abundance exceeds that seen in almost all known comets from our own solar system.

From Science Daily ● Sep. 9, 2026

Meteor showers happen when the Earth passes through trails of debris from asteroids or comets - a snowball of frozen rock and gas orbiting the Sun.

From BBC ● Aug. 11, 2026

Another branch of their work is planetary defence, which involves identifying threats like comets and asteroids.

From Barron's ● Aug. 7, 2026

From about 4.56 billion to 3.5 billion years ago, meteorites, micrometeorites and interplanetary dust particles from asteroids and comets repeatedly struck Earth.

From Science Daily ● Jul. 19, 2026

I searched the skies for flaming comets, for that was how I pictured a cannonball would look.

From "Chains" by Laurie Halse Anderson