'apoapsidal' originates from New Latin/scientific formation built from the noun 'apoapsis', where Greek 'apo-' meant 'away from' and Greek 'apsis' meant 'arch' or 'loop' (used for an orbital extremity).

'apoapsidal' developed by adding the English adjective-forming suffix '-al' to 'apoapsis'. 'Apoapsis' entered scientific English from New Latin 'apoapsis', ultimately from Greek 'apoapsis'.

Initially it meant 'pertaining to the apoapsis (the farthest point of an orbit)', and over time it has retained this technical meaning in astronomy and astrodynamics.