ENGLISH
REFERENCE

asteroid

n.
US //ˈæstɝˌɔɪd// UK //ˈɑːstəɹˌɔɪd// as·ter·oid
  1. 1 space rock (n.)
    B2 Upper Intermediate Science

    a large piece of rock or metal that moves around the sun, mostly in the space between Mars and Jupiter.

    a small rocky or metallic body orbiting the sun, typically found in the asteroid belt between Mars and Jupiter.

    Example

    Scientists are tracking a large asteroid that will pass close to Earth next month.

    Example

    The mission aimed to land a probe on the asteroid's surface to analyse its mineral composition and determine its origin within the early solar system.
    • planetoid
    • minor planet
  2. 2 starfish (n.)
    C2 Proficiency Technical Science

    a sea animal with a flat, star-shaped body and five or more arms.

    any echinoderm of the class Asteroidea, characterised by a flattened body and radiating arms.

    Example

    The diver found a bright red asteroid clinging to the side of the coral reef.

    Example

    Marine biologists observed the asteroid using its tube feet to pry open the shell of a bivalve during the feeding cycle.

    Usage

    In modern general English, 'starfish' or 'sea star' is almost always preferred over 'asteroid'.
Etymology 1

From aster + -oid, lit. "star-like". Coined by William Herschel.

Etymology 2

Borrowed from Ancient Greek ἀστεροειδής (asteroeidḗs), from ἀστήρ (astḗr, “star”) + εἶδος (eîdos, “form”). Analyzable as aster- + -oid. Piecewise doublet of etymology 1. Compare also the botanical taxon Asteroideae.

Etymology adapted from Wiktionary, available under CC BY-SA 4.0.

Related words

Last updated June 20, 2026