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.
Examples from the Web for bann
Says Corder, struggling with his pack, “Bann, will you help me into my corset.”At Plattsburg
To him the sources of most human consolations "were barr'd and bann'd, forbidden fare."Coleridge
Samuel Levy Bensusan
He met Tirlogh Luineach at the Bann, and thought him inclined to obey.Ireland Under the Tudors, Vol. II (of 3)
There is, for instance, the drainage of the Barrow and the Bann.The Open Secret of Ireland
T. M. Kettle
A year or two later, however, machinery was introduced on a large scale on the river Bann.