An Etymological Dictionary of Astronomy and Astrophysics

The point of greatest or least distance of the orbit of a celestial body from a center of attraction. The closest point is the → periapsis, the further point the → apoapsis.

Etymology (EN): L. apsis “arch, vault,” from Gk. hapsis “loop, arch,” from haptein “fasten together”.

Etymology (PE): Mod.Pers. habâk “top of the head; the summit of a mountain”.