From Longman Dictionary of Contemporary Englishsworn enemiessworn enemiesx-reftwo people or groups of people who will always hate each other → sworn
Examples from the Corpus
sworn enemies• In the Fifties they were sworn enemies.• This killer dressed like a popinjay, sweetly singing a madrigal to men he knew were his sworn enemies.• It is a strange sister party which wants to see Labour's sworn enemies back in power.• Also playing a key role as protagonists and unlikely allies are two former sworn enemies, both ladinos.• More and more the sworn enemies of Tokugawa political power openly flouted Bakufu authority.• One minute they were sworn enemies, the next they were clinging together in fierce mutual desire. 