/keuh loor", koh-, koh"loor/ , n. Astron.
either of two great circles of the celestial sphere intersecting each other at the poles, one passing through both equinoxes and the other through both solstices.
[ 1540-50; colurus kólouros dock-tailed, equiv. to kól ( os ) docked + -ouros -tailed, adj. deriv. of ourá tail; so called because the lower part is permanently hidden beneath the horizon ]