Mac Donagh - Mac Donnchadha (son of Donagh): A branch of the MacDermots of Connacht where the name is very numerous. In Connemara the name is usually that of a branch of the O’Flahertys. The MacDonagh sept in Co. Cork were a branch of the McCarthys: the name is now rare there and apparently many of these resumed the name MacCarthy.
O’Donnell - Ó Domhnaill: The main sept, one of the most famous in Irish history, especially in the seventeenth century, is of Tirconnell; another is of Thomond and a third of the Uí Maine.
(O) Donoghue - Donohoe ÓDonnchadha: An important sept in Desmond: where the name was perpetuated in the territory called Onaght O’Donoghue. There also were two others in County Galway and Co. Cavan where the spelling Donohoe is usual. According to Dr. John Ryan there was another O’Donoghue sept in Co. Tipperary of Eoghanacht. Descent.
Mac Dowell - Mac Dubhghaill (dubh, black-gall, foreigner): This is the Irish from of the name of the Scottish family of Macdugall which came from the Hebrides of galloglasses, and settled in Co. Roscommon where Lismacdowell locates them. It is now mainly found in north Ulster, largely due to more recent immigration.
(O) Duffy - ÓDubhthaigh: A numerous name in all the provinces except Munster. Modern statistics show that is now the most numerous name in Co. Monaghan.
(O) Dwyer - Ó Duibhir (dubh and odhar, gen. uidhir, duncoloured): Of Kilnamanagha, a leading sept in mid-Tipperary. A great name is resistance to English domination.
Mac Fadden - Fayden Mac Pháidín(Paídí n, a diminutive of Pádraig, Patrick): An Ulster name, of both Scottish and Irish origin. Without the Mac it is found in Mayo.
Fanning - Fannin Fainín: A Name of Norman origin prominent in Co. Limerick where Fanningstown, formerly of Ballyfanning, indicates the location. They were formerly of Ballingarry, Co. Tipperary, where in the fifteenth century the head of the family was, like Irish chiefs, officially described as ‘captain of his nation’. Fannin is a variant.
Fitzgerald - Mac Gerailt. One of the two greatest families which came to Ireland as a result of the Anglo-Norman invasion. It had two main divisions, Desmond (of whom are the holders of the ancient titles Knight of Kerry and Knight of Glin); and Kildare, whose leaders held almost regal sway up to the time of the Rebellion of Silken Thomas and the execution of Henry VIII of Thomas and his near relatives in 1537. The bane is now very numerous.
Fitzpatrick - Mac Giolla Phádraig (devotee of St. Patrick): The only Fitz name of Gaelic-Irish origin, the main sept being located in Ossory. The name is numerous also in Fermanagh where families so called are said to be of MacGuire stock.
Flanagan - Ó Flannagáin (flann, ruddy or red): Of the several septs of the name that of Connacht is the most important: their chief ranked as one of the ‘royal lords’ under O’Connor, King of Connacht.
Flood: Some Floods are of English extraction, but in Ireland they are plainly Ó Maoltuile or Mac Maoltuile, abbreviated to Mac an Tuile and Mac Tuile anglicized MacAtilla or MacTully as well as Flood. Tuile means flood but probably it is here for toile, gen. of toil, will, i.e. the will of God. In parts of Ulster Flood is used for the Welsh Floyd. (Welsh llwyd. Grey)
(O) Flynn - Flyng ÓFloinn (flann, ruddy): This numerous and widespread name originated in a number of different places, including Kerry and Clare. Of the two in Co. Cork one was a branch of the Corca Laoidhe, the other, lords of Muskerylinn (Muiscre Uí Fhloinn); in north Connacht the O’Flynns were leading men under the royal O’Connors, and there was also an erenagh family there; while further West on the shores of Lough Conn another distinct erenagh family was located. For the name in Ulster is an indigenous sept.
(O) Gallagher - ÓGallchobhair. This name (gallchobhar, foreign help): has at least 23 variant spellings in anglicized forms, several of them beginning with Gol instead of Gal. It is that of one of the principal septs of Donegal.
MacGowan - Mac an Ghabhann, Mac Gabhann: In Co. Cavan, the homeland of this sept, the name has been widely changed by translation to Smith (though Smithson was a truer translation); but in outlying areas of Breffny MacGowan is retained.
(O) Grady - Ó Grádaigh (gráda, illustrious): A Dalcassian sept. The leading family went to Co. Limerick but the majority are still Clare where the prefix O is retained more than anywhere else. An important branch changed their name to Brady in the late sixteenth century. The well-known name Grady has to a large extent absorbed the rarer Gready which is properly a Mayo name. This resulted in the name of Grady being numerous in north Connacht and adjacent areas of Ulster.