apsis

noun

ap·sis | \ ˈap-səs

plural apsides\ -sə-ˌdēz

Definition of apsis

1 : the point in an astronomical orbit at which the distance of the body from the center of attraction is either greatest or least

2 : apse sense 2

History and Etymology for apsis

borrowed from Medieval Latin apsīs, apsīda "arc, vault," going back to Latin apsīd-, apsīs (also hapsīs, absīs) "arc described by a planet, segment of a circle," borrowed from Greek hapsīd-, hapsís (Ionic apsís) "loop, mesh, rim of a wheel, wheel, disk, segment cut off by a rainbow, arch, vault," from ap-s-, stem in noun derivation of háptein "to fasten," háptesthai "to fasten oneself to, grasp" + -īd-, -īs, noun suffix — more at haptics