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”; see 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

NASA’s Amit Kshatriya, the man behind Artemis, on the race with China to reach Mars, the asteroid belt and Jupiter’s moons.

From The Wall Street Journal • May 15, 2026

We would hop into flying “aero sedans” that folded into briefcases and take holidays on an asteroid.

From The Wall Street Journal • May 15, 2026

NASA’s Amit Kshatriya, the man behind Artemis, on the race with China to reach Mars, the asteroid belt and Jupiter’s moons.

From The Wall Street Journal • May 15, 2026

NASA's OSIRIS-REx mission, which visited the asteroid Bennu, observed material erupting from the asteroid's surface.

From Science Daily • May 14, 2026

“I’m only saying,” said Gregory Powell, patiently, as one explaining electronics to an idiot child, “that according to spec, those robots are equipped for asteroid mining without supervision. We’re not supposed to watch them.”

From "I, Robot" by Isaac Asimov

Related Words

• earth
• globe
• sphere
• world