Definition of asteroid in US English:



  • 1A small rocky body orbiting the sun. Large numbers of these, ranging in size from nearly 600 miles (1,000 km) across (Ceres) to dust particles, are found (as the asteroid belt) especially between the orbits of Mars and Jupiter, though some have more eccentric orbits, and a few pass close to the earth or enter the atmosphere as meteors.

    • ‘Both comets and asteroids are the left-over building blocks of the planets in our solar system.’
    • ‘It's just that you can't keep quiet about things like asteroid impacts.’
    • ‘Comets and asteroids also contribute to the near-Earth space environment.’
    • ‘Ceres was initially considered to be a planet until other asteroids with similar orbits were found.’
    • ‘Fragments of asteroids and comets pervade interplanetary space.’
    • ‘There may be other families of small asteroids within our solar system that, even now, remain to be discovered.’
    • ‘In many ways asteroids and comets are likely to offer more varied and abundant natural resources than the Moon.’
    • ‘Dinosaurs may not have been killed off by asteroid impact dust blocking out sunlight, a geologist says.’
    • ‘When the asteroid hit, it was vaporized by the extreme energy of the impact.’
    • ‘These scientists also study the natural satellites of other planets as well as asteroids and comets.’
    • ‘So to neglect the problem means that we are vulnerable to asteroid collisions.’
    • ‘These glaciers are spotted with craters caused by asteroid impacts.’
    • ‘Most of the known asteroids orbit the sun in a belt between Mars and Jupiter.’
    • ‘You can also get asteroid hazard warnings and geomagnetic storm outlooks.’
    • ‘In our own solar system, asteroids have collided with Earth, the moon and other planets.’
    • ‘Some explanations for extinctions and evolution include strikes by asteroids or comets.’
    • ‘It has been suggested that impacts with comets and asteroids provided Earth with much of its water.’
    • ‘Most of the larger asteroids and comets are also in stable orbits around the sun.’
    • ‘Amateur astronomers have made many asteroid, comet, and supernova discoveries.’
    • ‘We know very little about these families of asteroids following the same orbit.’
    • ‘Our knowledge of comets and asteroids has dramatically improved over the last 20 years.’
    • ‘Our star system is chock full of asteroids and comets, in every conceivable orbit and location.’
    • ‘Once an asteroid drifts into either of those regions, it's hard for it to get out.’
    celestial body, heavenly body, sun
    View synonyms
  • 2Zoology
    An echinoderm of the class Asteroidea, which comprises the starfishes.

    • ‘Available morphological data suggest no ecologic parameters that would be unusual among living asteroids.’
    • ‘Both approaches will shed light on the adaptive significance and functional morphology of asteroids.’
    • ‘The fossil record is a potential source of needed data, although fossil asteroids are rare, and they tend to be poorly preserved.’
    • ‘The asteroid is preserved with the dorsal surface exposed.’
    • ‘An unpaired commonly enlarged interbrachial ossicle, the axillary, occurs in most Paleozoic asteroids, including those treated here.’


  • Relating to or denoting echinoderms of the class Asteroidea.


Early 19th century: from Greek asteroeidēs ‘starlike’, from astēr ‘star’.