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
There is, for instance, the drainage of the Barrow and the Bann.The Open Secret of Ireland|T. M. Kettle
He met Tirlogh Luineach at the Bann, and thought him inclined to obey.Ireland Under the Tudors, Vol. II (of 3)|Richard Bagwell
To him the sources of most human consolations "were barr'd and bann'd, forbidden fare."Coleridge|Samuel Levy Bensusan
And when known by his wife and children, in this way, they were put under the bann of secrecy.A Walk from London to John O'Groat's|Elihu Burritt
There are fisheries for salmon and eels on the Bann, for which Coleraine is the headquarters.