'archenemy' originates from a combination of the prefix 'arch-' and the noun 'enemy'. The prefix 'arch-' comes from Greek 'arkhós' (via Old French/Middle English) where 'arkhós' meant 'chief' or 'principal', and 'enemy' comes from Old French 'enemïe' (from Latin 'inimicus') where 'inimicus' meant 'not a friend'.

'archenemy' developed in Middle English as a compound of 'arch-' + 'enemy' (Middle English forms such as 'arch-enemi') and eventually became the modern English word 'archenemy'.

Initially, the compound simply meant 'chief enemy' and over time it has retained that sense, coming to denote a principal or most important enemy or rival.