WordReference Random House Unabridged Dictionary of American English © 2026
Oort′ cloud′
(ôrt, ōrt),USA pronunciation [Astron.]
- Astronomya region of the solar system far beyond the orbit of Pluto in which billions of comets move in nearly circular orbits unless one is pulled into a highly eccentric elliptical orbit by a passing star.
- after Dutch astronomer Jan Hendrik Oort (1900–1992), who proposed its existence 1975–80