What is "magennis"

Magennis also spelled Maguiness, Maginnis, McGuinness or Guinness, is an Irish surname, meaning the "descendants of Angus", which in eastern Ulster was commonly pronounced in Irish as Mag Aonghusa. A prominent branch of the Uíbh Eachach Cobha, the Magennises would become chiefs of the territory of Iveagh, which by the 16th century comprised over half of modern County Down, Northern Ireland. By the end of the 17th century, their territory had been divided up between them and British prospectors.

The four main branches of the Magennis clan were: Castlewellan, Corgary, Kilwarlin, and Rathfriland, of which there was rivalry between. The Mac Artáin (MacCartan) sept of Kinelarty, descend from the Magennis clan, through the great-grandson of Mongán Mac Aonghusa.