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

Explanation

An asteroid is a large, irregularly shaped object in space that orbits our Sun. If one of these giant rocks ends up on a collision course with Earth, we are in for big trouble. An asteroid is like a comet. However, while comets are mostly made of ice, asteroids are made up of rock or even metal. This makes them dangerous because they can cause a lot of damage if they collide with a planet. The craters on the Moon were formed by asteroids and some think it was an asteroid that wiped out the dinosaurs. Around a million asteroids are located between Mars and Jupiter in an area called the “asteroid belt.”

Example Sentences

There are vitrines throughout, filled with fine jewelry, asteroid chunks and a brontosaurus tooth; some of them have drink rails, where a martini can rest beside an artifact that’s hundreds of millions of years old.

From The Wall Street Journal • Apr. 14, 2026

John Maclean, from the UK Meteor Network, said the meteor was not connected to any astronomical event, and likely stemmed from a larger asteroid.

From BBC • Apr. 13, 2026

Another lamented that they cry at the end of every dino doc, even though they know the asteroid is coming and extinction is on the horizon.

From Salon • Apr. 12, 2026

In a classic episode, Elroy goes to an asteroid on a school field trip.

From The Wall Street Journal • Mar. 30, 2026

Though the asteroid is given the provisional designation 2016BA11 until its orbit can be confirmed, Frieda knows she will name it the Jürgen Eichman in honor of him.

From "We Are the Ants" by Shaun David Hutchinson

Related Words

• earth
• globe
• sphere
• world