colure

noun

either of two great circles of the celestial sphere intersecting each other at right angles at the celestial poles: one passes through the solstices (solstitial colure), the other through the equinoxes (equinoctial colure)

Etymology: < L coluri < Gr kolouroi, the colures, lit., dock-tailed (ones), pl. of kolouros < kolos, docked (see holt) + oura, tail (see uro-): the “tail” (i.e., the lower part) is cut off from view by the horizon