'apsis' originates from Greek, specifically the word 'hapsis' (Greek ἁψίς), where 'hapsis' meant 'arch' or 'loop'.

'apsis' passed into Latin/Medieval Latin as 'apsis' and was adopted into English; the plural form 'apsides' follows the Greek/Latin plural formation.

Initially it meant 'arch' or 'loop' in Greek, but over time it came to be used in astronomy to denote the extreme point(s) of an orbit (greatest or least distance).