Ó Diamáin
Ó DIAMÁIN—I—O'Diamain, Diaman, Diamon, Diamond, Dimond; 'descendant of Diamán' or 'Déamán' (more correctly Díomán, diminutive of Díoma, a personal name); the name of an old ecclesiastical family in Ulster who were erenaghs of Kilrea, in Co. Derry, and are still numerous in Derry and Antrim.
Alphabetical Index to Irish Surnames