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:
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
Japan also has experience in bringing back samples from space, including JAXA's unmanned Hayabusa-2 which returned 5.4 grams of rock and dust collected from an asteroid several hundred million kilometres from Earth in 2020.
From Barron's ● Aug. 16, 2026
"Asteroids are a really interesting challenge in many ways. It's unusual for an asteroid to come out of nowhere," explained Nash.
From Barron's ● Aug. 7, 2026
A future supply network could move metals from asteroids to Mars while using propellant produced from asteroid resources.
From Science Daily ● Aug. 7, 2026
When the zigzagging UFO comes he lays in a salvo of torpedoes only if the asteroid storm isn't too heavy.
From "Black Swan Green" by David Mitchell
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
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
Nobody knows even approximately how many asteroids there are tumbling through space, but the number is thought to be probably not less than a billion.
From "A Short History of Nearly Everything" by Bill Bryson
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.
