Search Result for "oort cloud":
Wordnet 3.0

NOUN (1)

1. (astronomy) a hypothetical huge collection of comets orbiting the sun far beyond the orbit of Pluto; perturbations (as by other stars) can upset a comet's orbit and may send it tumbling toward the sun; 



WordNet (r) 3.0 (2006):

Oort cloud
    n 1: (astronomy) a hypothetical huge collection of comets
         orbiting the sun far beyond the orbit of Pluto;
         perturbations (as by other stars) can upset a comet's orbit
         and may send it tumbling toward the sun