'aphelionic' originates from New Latin/Greek, specifically the word 'aphelion', where the Greek elements 'apo-' (away from) and 'hēlios' (sun) combine to mean 'away from the sun'.

'aphelion' comes from Greek 'aphélion' and passed into New Latin as 'aphelion'; the English adjective 'aphelionic' was later formed by adding the adjectival suffix '-ic' to the noun 'aphelion'.

Initially it denoted the noun 'the point in an orbit farthest from the sun'; over time the derived adjective came to mean 'relating to or at that farthest point'.