'Athenian' originates from Greek, specifically the word 'Athēnai' (Ἀθῆναι), the name of the city of Athens; the English adjectival/denominative suffix '-ian' (via Latin/French) was added to form 'Athenian'.

'Athenian' changed through Latin and Old French forms (e.g. medieval Latin/Old French forms meaning 'of Athens') and appeared in Middle English (e.g. Middle English 'Athenien'), eventually becoming the modern English 'Athenian'.

Initially it meant 'of or belonging to Athens' and that core meaning has remained largely stable, applying both to ancient and modern contexts.