'archfiend' originates from Late Middle English, formed from the prefix 'arch-' (from Greek 'arkhi-' meaning 'chief') and the word 'fiend' (from Old English 'fēond' meaning 'enemy' or 'demon').

'fiend' comes from Old English 'fēond' meaning 'enemy'; the prefix 'arch-' derives from Greek 'arkhi-' via Latin/Old French as 'archi-'; these elements combined in Late Middle English to produce 'archfiend'.

Initially it meant 'chief enemy' or 'principal demon'; over time it came to mean specifically 'chief devil' and, by extension, 'a very wicked person' or 'arch-enemy' in figurative use.