asteroid

American  

[as-tuh-roid] / ˈæs təˌrɔɪd /

noun

1. 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.

2. Zoology. a starfish; an asteroidean.

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adjective

1. starlike.

asteroid British  

/ ˈæstəˌrɔɪd /

noun

1. 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

2. Also called: asteroidean.  any echinoderm of the class Asteroidea; a starfish

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adjective

1. of, relating to, or belonging to the class Asteroidea

2. shaped like a star

asteroid Scientific  

/ ăs′tə-roid′ /

1. 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.

2. Also called minor planet planetoid

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asteroid Cultural  

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

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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

The asteroid itself is made up of fragments from a much larger parent body that broke apart long ago.

From Science Daily • Mar. 31, 2026

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

"Large impact basins or craters excavate deep into the asteroid, which gives clues about what its interior is made of," said Namya Baijal, a doctoral candidate at the LPL and first author of the paper.

From Science Daily • Mar. 17, 2026

She used telescopes to study near-Earth asteroids—those close enough to the edge of the asteroid belt that they could escape and come toward Earth!

From "Sir Fig Newton and the Science of Persistence" by Sonja Thomas

Related Words

• earth
• globe
• sphere
• world