'athanasian' originates from Greek, specifically the name 'Athanásios' (Ἀθανάσιος), where the prefix 'a-' meant 'not' and 'thanatos' meant 'death' (together giving the sense 'immortal').

'athanasian' was formed in English from the Latinized name 'Athanasius' (from Medieval/Church Latin 'Athanasius'), itself from Greek 'Athanásios'; the English adjectival form was created by adding the suffix '-an' to the proper name.

Initially it meant 'of or pertaining to Athanasius (the person)', but over time it came also to mean 'relating to doctrines associated with Athanasius' and specifically to the Athanasian Creed and its formulations about the Trinity.