asteroid
Americannoun
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asteroids
plural
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Astronomy. any of millions of small celestial objects revolving around the sun, often irregularly shaped and having a great range in size, from as small as 6 feet (2 meters) across to about 620 miles (998 kilometers) across: the vast majority of known asteroids exist within the asteroid belt.
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Zoology. a starfish; an asteroidean.
adjective
noun
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Also called: minor planet, planetoid. any of numerous small celestial bodies that move around the sun mainly between the orbits of Mars and Jupiter. Their diameters range from 930 kilometres (Ceres) to less than one kilometre
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Also called: asteroidean. any echinoderm of the class Asteroidea; a starfish
adjective
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of, relating to, or belonging to the class Asteroidea
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shaped like a star
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Any of numerous small solar system bodies that orbit the Sun primarily in the asteroid belt, a region between the orbits of Mars and Jupiter. Asteroids are intermediate in size between planets and meteoroids with diameters that measure between approximately one hundred and several hundred kilometers. While more than 1,800 asteroids have been cataloged, and as many as a million or more smaller ones may exist, their total mass has been estimated to be less than three percent of the Moon's. Asteroids are thought to be left over from the early formation of the solar system, when planetesimals in a protoplanetary disk were scattered after coming under Jupiter's gravitational influence. The continuing collision of planetesimals that remained between Jupiter and Mars caused many of them to fragment, creating the asteroids that exist today.
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Also called minor planet planetoid
Other Word Forms
Derived Forms
Inflected Forms
Nouns
Etymology
Origin of asteroid
First recorded in 1795–1805; from Greek asteroeidḗs “starry, starlike”; see star, -oid
Explanation
An asteroid is a large, irregularly shaped object in space that orbits our Sun. If one of these giant rocks ends up on a collision course with Earth, we are in for big trouble. An asteroid is like a comet. However, while comets are mostly made of ice, asteroids are made up of rock or even metal. This makes them dangerous because they can cause a lot of damage if they collide with a planet. The craters on the Moon were formed by asteroids and some think it was an asteroid that wiped out the dinosaurs. Around a million asteroids are located between Mars and Jupiter in an area called the “asteroid belt.”
Vocabulary lists containing asteroid
Over The Moon: Planetary Vocabulary
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Oh, My Stars! A Solstice Sampler
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Elements of the Universe: Aster, Astro ("Star")
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
See Examples For:
Their spectral properties, along with models of asteroid capture, provide support for that possibility, according to the researchers.
From Science Daily ● Sep. 19, 2026
One hypothesis has proposed that Neornithes survived because many lived around aquatic environments, where conditions may have offered some protection from the devastation following the asteroid impact.
From Science Daily ● Sep. 11, 2026
According to the researchers, an asteroid about 320 meters across striking Deimos at an angle of 45 degrees could have produced the size and shape of the depression now visible near the moon's south pole.
From Science Daily ● Aug. 26, 2026
The Little Prince, who lives on a house-sized asteroid, recounts his travels to different planets and shares solemn wisdom about life’s challenges.
From The Wall Street Journal ● Aug. 17, 2026
They were bronzy gleams of smooth motion against the shadowy crags of the airless asteroid.
From "I, Robot" by Isaac Asimov
The Exoasteroids project gives citizen scientists the chance to look for evidence of asteroids beyond our Solar System.
From Science Daily ● Sep. 22, 2026
The Daily Minor Planet project allows volunteers to help search for asteroids and comets that could potentially pose a threat to Earth.
From Science Daily ● Sep. 22, 2026
The "capture" hypothesis meanwhile postulates that the moons are asteroids from the outer Solar System that were captured by Mars' gravity.
From Barron's ● Aug. 16, 2026
This occurs when the Earth passes through trials of debris from asteroids or comets.
From BBC ● Aug. 12, 2026
Perhaps a trip from Libra to one of the asteroids would bring back materials rich in carbon and nitrogen.
From "Flying to the Moon: An Astronaut's Story" by Michael Collins
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
