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[as-tuh-roid] /ˈæs təˌrɔɪd/
Also called minor planet. Astronomy. any of the thousands of small bodies of from 480 miles (775 km) to less than one mile (1.6 km) in diameter that revolve about the sun in orbits lying mostly between those of Mars and Jupiter.
Zoology. an asteroidean; a starfish.
Origin of asteroid
1795-1805; < Greek asteroeidḗs starry, starlike. See asterisk, -oid
Related forms
asteroidal, adjective
interasteroidal, adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the web for asteroids
  • asteroids, moons and comets have all been added to the stamp album.
  • With such objects, and with asteroids, several observations are required in order to pin down an accurate orbit.
  • These scars from the impact of speeding comets and asteroids were simply too fresh and too few and too random.
  • asteroids and comets in nearby space pose a constant threat to our planet.
  • In addition, there are thousands of small bodies such as asteroids and comets.
  • Meteoroids, in particular, are fragments of asteroids produced by collisions.
  • In general, asteroids are heated by the decay of radioactive atoms scattered throughout their insides.
  • Most asteroids are chunks of metallic rock that have virtually no atmospheres.
  • The rings of asteroids contain rocky, raw materials leftover from the formation of planets.
  • But it's been unclear whether the impactors were icy comets or rocky asteroids.
British Dictionary definitions for asteroids


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
Also called asteroidean (ˌæstəˈrɔɪdɪən). any echinoderm of the class Asteroidea; a starfish
of, relating to, or belonging to the class Asteroidea
shaped like a star
Word Origin
C19: from Greek asteroeidēs starlike, from astēr a star
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for asteroids



1802, coined probably by German-born English astronomer William Herschel (1738-1822) from Greek asteroeides "star-like," from aster "star" (see astro-) + -eidos "form, shape" (see -oid).

Online Etymology Dictionary, © 2010 Douglas Harper
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asteroids in Science
Any of numerous small, often irregularly shaped rocky 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; the largest asteroid in the asteroid belt is Ceres, approximately 1,000 km (620 mi) in diameter, while the lower limit is variously given in the tens or hundreds of meters. 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. Also called minor planet, planetoid.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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asteroids in Culture
asteroid [(as-tuh-royd)]

A small planet that revolves around the sun. The largest asteroid is only about six hundred miles in diameter. (See asteroid belt.)

The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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