Search Result for "planetesimal": 
Wordnet 3.0

NOUN (1)

1. one of many small solid celestial bodies thought to have existed at an early stage in the development of the solar system; 



WordNet (r) 3.0 (2006):

planetesimal
    n 1: one of many small solid celestial bodies thought to have
         existed at an early stage in the development of the solar
         system