Where does “ἀμερμουμνῆς” come from?

ἀμερμουμνῆς (Byzantine Greek) comes from Arabic أَمِير الْمُؤْمِنِين, from Arabic أَمِير — prince; prince; commander; commander, prince.

ἀμερμουμνῆς (Byzantine Greek): a caliphal title used to denote legitimacy in the...