The Collaborative International Dictionary of English v.0.48:

Asteroid \As"ter*oid\, n. [Gr. ? starlike, starry; 'asth`r star
   + e'i^dos form: cf. F. ast['e]ro["i]de. See Aster.]
   A starlike body; esp. one of the numerous small planets whose
   orbits lie between those of Mars and Jupiter; -- called also
   planetoids and minor planets.
   [1913 Webster]

WordNet (r) 3.0 (2006):

asteroid
    adj 1: shaped like a star [syn: asteroid, star-shaped]
    n 1: any of numerous small celestial bodies composed of rock and
         metal that move around the sun (mainly between the orbits
         of Mars and Jupiter)

Moby Thesaurus II by Grady Ward, 1.0:

31 Moby Thesaurus words for "asteroid":
   Earth, Jupiter, Mars, Mercury, Neptune, Pluto, Saturn, Uranus,
   Venus, asteroids, aurora particles, blackout, cosmic particles,
   cosmic ray bombardment, inferior planet, intergalactic matter,
   major planet, meteor dust impacts, meteors, minor planet, planet,
   planetoid, radiation, secondary planet, solar system,
   space bullets, superior planet, terrestrial planet, the bends,
   wanderer, weightlessness