WordReference Random House Learner's Dictionary of American English © 2017
as•ter•oid /ˈæstəˌrɔɪd/USA pronunciation   n. [countable]
  1. Astronomyany of the small, solid bodies that revolve about the sun in orbit chiefly between Mars and Jupiter.
See -astro-.
WordReference Random House Unabridged Dictionary of American English © 2017
as•ter•oid  (astə roid′),USA pronunciation n. 
  1. AstronomyAlso called  minor planet. any of the thousands of small bodies of from 480 miles (775 km) to less than one mile (1.6 km) in diameter that revolve about the sun in orbits lying mostly between those of Mars and Jupiter.
  2. Invertebrates[Zool.]an asteroidean;
    a starfish.

  1. starlike.
as′ter•oidal, adj. 
  • Greek asteroeidé̄s starry, starlike. See asterisk, -oid
  • 1795–1805

Collins Concise English Dictionary © HarperCollins Publishers::

asteroid /ˈæstəˌrɔɪd/ n

  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 /ˌæstəˈrɔɪdɪən/ any echinoderm of the class Asteroidea; a starfish
Also: asteroidal /ˌæstəˈrɔɪdəl/
  1. of, relating to, or belonging to the class Asteroidea
  2. shaped like a star
Etymology: 19th Century: from Greek asteroeidēs starlike, from astēr a star

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