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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.
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 asteroid
  • It is the first discovered natural satellite of a larger asteroid.
  • Then one day a big, bad asteroid came along and wiped out all the dinosaurs.
  • Astronomers have discovered a unique set of triplets: an asteroid with two moons orbiting it.
  • For the first time, scientists were able to track an asteroid from space to the ground and recover pieces of it.
  • Please wait a moment for the asteroid applet to complete loading.
  • By now it is common knowledge that the impact of an asteroid or comet brought the age of the dinosaurs to an abrupt end.
  • Water ice and organic molecules have been discovered on the surface of an asteroid for the first time.
  • Most meteorites are thought to originate in the asteroid belt.
  • Telescopes spy the closest asteroid flyby ever recorded.
  • Dinosaurs may ultimately have been killed off not by a huge asteroid but by tiny germs.
British Dictionary definitions for asteroid


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 asteroid

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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asteroid 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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asteroid 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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