Help With 13th Century Seal Translation (of HOINU)

Hello Latinists!

I respectfully ask for some help in translating a legend of an old seal, as one word I cannot seem to find a English equivalent (hoinu). Although a Google search does result in a few hits, nothing of a translation is provided.

The legend is as: "S. SERIE HOINU DUCIS DE LEBOR JURAT. DELT." Overall, these are men of a council who swear to uphold and execute the laws of the duke. Am I on the right track? In either case, I cannot find the word, or an inflection of "honiu," therefore cannot complete the translation.

Any help would be much appreciated.