Apsis

ap′sis, n. one of the two extreme points in the orbit of a planet, one at the greatest, the other at the least distance from the sun: one of the two points in the orbit of a satellite—one nearest to, the other farthest from, its primary; corresponding, in the case of the moon, to the perigee and apogee:— pl. Apsides (ap′si-dēz). — adj. Ap′sidal . [L. apsis —Gr. haps is , a connection, an arch— hapt-ein , to connect. See Apt .]