'archdevil' is formed from the combining element 'arch-' (ultimately from Greek 'arkhos' meaning 'chief' or 'principal') and the noun 'devil' (from Old English 'deofol').

'devil' comes from Old English 'deofol', from Late Latin 'diabolus', from Greek 'diabolos' ('dia-' meaning 'across, through' + 'ballein' meaning 'to throw'); 'arch-' comes from Greek 'arkhos' ('chief') and was adopted into English as a combining form, producing the compound 'archdevil' in English usage.

Initially the compound simply denoted the 'chief devil' (a principal demon); over time it retained that theological sense and also acquired a figurative sense meaning an especially wicked or notorious person.