bann (n.)youdaoicibaDictYouDict[bann 词源字典]
in phrase banns of marriage (late 12c., spelling with double -n- attested from 1540s), from Old English bannan "to summon, command, proclaim" (see ban (v.)). Also probably partly from Old French ban "announcement, proclamation, banns, authorization," from Frankish *ban or some other Germanic cognate of the Old English word.[bann etymology, bann origin, 英语词源]