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)