'aniseikonic' originates from New Latin/Greek, specifically the Neo-Greek medical word 'aniseikonía', where 'an-' meant 'not' (or 'without'), 'is(o)-' meant 'equal' and 'eikon' meant 'image', with the English adjectival suffix '-ic' forming 'aniseikonic'.

'aniseikonic' changed from the Neo-Greek/New Latin noun 'aniseikonía' (meaning the condition of unequal images) and entered English usage in ophthalmic literature; the adjectival form 'aniseikonic' was later derived from that noun.

Initially, it meant 'the condition of unequal image size between the two eyes' (the noun 'aniseikonia'), but over time it has also come to be used adjectivally to mean 'pertaining to or caused by aniseikonia' (i.e., 'aniseikonic').