asteroid
Americannoun
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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
- asteroidal adjective
- interasteroidal adjective
Etymology
Origin of asteroid
First recorded in 1795–1805; from Greek asteroeidḗs “starry, starlike”; star, -oid
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.
In a classic episode, Elroy goes to an asteroid on a school field trip.
From The Wall Street Journal • Mar. 30, 2026
In their simulations, the asteroid was struck at speeds typical for the asteroid belt, about three miles per second.
From Science Daily • Mar. 17, 2026
More than two centuries after asteroid 16 Psyche was first identified, scientists are still trying to determine how it formed.
From Science Daily • Mar. 17, 2026
About 66 million years ago, a massive asteroid struck Earth and unleashed one of the most destructive events in the planet's history.
From Science Daily • Mar. 15, 2026
They were bronzy gleams of smooth motion against the shadowy crags of the airless asteroid.
From "I, Robot" by Isaac Asimov
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.
