ˈō(ə)rt-, ˈȯrt- noun
Usage: usually capitalized O
Etymology: after Jan Oort died 1992 Dutch astronomer
: a spherical shell of cometary bodies which is believed to surround the sun far beyond the orbit of Pluto and from which some are dislodged when perturbed (as by a passing star) to fall toward the sun — compare kuiper belt herein