'Athenian' originates from Greek, specifically the word 'Athēnai' (Ancient Greek 'Ἀθῆναι'), where the root referred to the city of Athens; it is formed with the Latin-derived suffix '-ian'/'-ianus' meaning 'belonging to' or 'from'.

'Athenian' changed from the Ancient Greek place-name 'Athēnai' into Late Latin/Medieval Latin forms (e.g. 'Athenianus') and was adopted into Middle English as 'Athenian', becoming the modern English adjective and noun.

Initially, it meant 'belonging to or from Athens' (the place name); over time it retained that meaning and also came to denote the people of Athens specifically.