This is all that we know of the origin of Irish surnames. Sir James Ware agrees with Keating and Gratianus Lucius that surnames became hereditary in Ireland in the tenth or beginning of the eleventh century; and adds, that they became hereditary in England and France about the same period. Irish family names or surnames then are formed from the genitive case of names of ancestors who flourished in the tenth century, and at later periods, by prefixing O, or Mac, as O’Neill, Mac Carthy, &c. O literally signifies grandson, in which sense it is still spoken in the province of Ulster; and in a more enlarged sense any male descendant, like the Latin _nepos_: and Mac literally signifies son, and in a more extended sense any male descendant. The former word is translated _nepos_ by all the writers of Irish history in the Latin language, from Adamnan to Dr O’Conor, and the latter, _filius_; from which it is clear that it is synonymous with the Welsh prefix _Map_ (abbreviated to _Ap_), and with the Anglo-Norman _Fitz_, which Horne Tooke has proved to be a corruption of the Latin _filius_. Giraldus Cambrensis latinizes the name of the King of Leinster, Dermot Mac Murchadh, _Dermitius Murchardides_, from which it may be clearly perceived that he regarded the prefix Mac as equivalent to the Greek patronymic termination _ides_. The only difference therefore to be observed between O and Mac in surnames is, that the family who took the prefix of Mac called themselves after their father, and those who took the prefix O formed their surname from the name of their grandfather. Ni, meaning daughter, was always prefixed to names of women, as O and Mac meant male descendants; but this usage is now obsolete. It is not perhaps an unlikely conjecture that at the period when surnames were first ordered to be made hereditary, some families went back several generations to select an illustrious ancestor on whom to build themselves a name. A most extraordinary instance of this mode of forming names occurred in our own time in Connaught, where John Mageoghegan, Esq. of Bunowen Castle, in the west of the county of Galway, applied to his Majesty King George IV. for licence to reject the name which his ancestors had borne for eight hundred years from their ancestor Eochagan, chief of Kinel Fiacha, in the now county of Westmeath, in the tenth century, and to take a new name from his more ancient and more illustrious ancestor Niall of the Nine Hostages, monarch of Ireland in the fourth century. His majesty granted this licence, and the son of John Mageoghegan now called John Augustus O’Neill, that is, John Augustus, DESCENDANT of Niall of the Nine Hostages. The other branches of the family of Mageoghegan, however, still retain the surname which was established in the reign of Brian Boru as the distinguishing appellative of the race of Fiacha, the son of Niall of the Nine Hostages, and the ancestor from whom the Mageoghegans had taken their _tribe_ name.