(O) Hagan - Ó hÁgáin. It is fairly well established that this name was originally Ó hÓgáin (from óg, young). It is that of an important Ulster sept: the leading family was of Tullahogue. Ó hAodhagáin, also anglicized O’Hagan, is said to be a distinct sep of Oriel, but owing to proximity of Co. Tyrone and Armagh, they are now indistinguishable. The Offaly name mentioned by Woulfe is now extinct or absorbed by Egan in Leinster. ÉO Dowd (a) Ó Dubhda. A branch settled in Kerry where they are called Doody. Another small sept of Ó Dubhda Co. Derry and they are usually Duddy now.
Hanlon - Ó hAluain (possibly from luan, champion, intensified by an) One of the most important of the septs of Ulster. The present association of the name with West Munster is of comparatively recent inception.
O'Hara - Ó hEaghra. An important dual sept located in Co. Sligo, the chiefs being O’Hara Boy (buidhe) and O’Hara Reagh (riabhach). A branch migrated to the glens of Antrim.
(O) Healy - Hely This is Ó hÉalaighthe in Munster, sometimes anglicized Healihy, and ÓhÉilidhe in north Connacht, derived respectfully from words meaning ingenious and claimant. Ballyhelyon Lough Arrow was the seat of the altar. The Munster sept was located in Donoughmore, Co. Cork, whence was taken the title conferred on the Protestant branch.
(O) Heaney - Heeney T he Principal sept of this name is Ó hÉighnigh in Irish, important and widespread in Oriel, formerly stretching its influence into Fermanagh. Hegney is a variant. Another family of the name Ulster were erenaghs of Banagher in Co. Derry. Minor septs of Ó hÉanna (Éanna, old form of Enda), also anglicized Heaney, were of some note in Clare, Limerick, and Mayo up to the seventeenth century.
(O) Higgins - Ó hUigín (from an Old-Irish word akin to Viking, not from uige). A sept of the southern Uí Néill which migrated to Connacht. The O’Higgins father and son of South American fame came from Ballinary, Co. Sligo, not Ballina.
(O) Hogan - Ó hÓgain (og, young) Three septs are so called: one is Dalcassian and one of Lower Dormond (sometimes regarded as the same); there is also one of the Corca Laoidhe.
Kane - O Cahan Ó Catháin. As lords of Keenaght the O’Kanes were a leading sept in Ulster up to the time of the plantation of Ulster. The name is still very numerous in its original homeland.
Keating - One of the earliest Hibernicized Anglo-Norman families whose name was gaelicized Ceitinn. They settled in south Leinster. The historian Dr. Geoffrey Keating was of C. Tipperary. The name with the prefix Mac is associated exclusively with the Downpatrick area, where MacKetian is a synonym of it. The theory that Keating is derived from Mac Eitienne is improbable. Woulfe makes it toponymic. The most acceptable suggestion is that it is from Cethyn, a Welsh personal name.
(O) Kelly - Ó Ceallaigh (The derivation of Kelly is uncertain: the most probable suggestion is that is from ceallach, strife) The most important and numerous sept of this name is that of the Uí Maine. Kelly is the second most numerous name in Ireland. In 1890 less than one percent of them had the prefix O but this has been to some extent resumed.
Mac Kenna - Kennagh Mac Cionaoith. A branch of the southern Uí Neill, mainly located in Co. Monaghan where they were lords of Truagh; the name is now fairly numerous also in Leinster and Munster. Locally in Clare and Kelly the last syllable is stressed, giving the variants Kennaw, Ginna, Gna, etc.
Kennedy - Ó Cinnéide (ceann, head-éidigh, ugly). An important Dalcassian sept of east Clare which settled in north Tipperary and spread thence far as Wexford whence came the family of President J.F. Kennedy. The Scottish Kennedys are by remote origin Irish Gaels.
Lawless - Laighléis (from the Old-English laghles, outlaw). The name, introduced into Ireland after the Anglo-Norman invasion, is now numerous in Co.s Dublin and Galway. It was one of the ‘Tribes of Kilkenny’ but has now no close association with the city.
(O) Leahy - Ó Laochdha (laochda, heroic). This name is very numerous in Munster but not elsewhere It is basically distinct from Lahy though they have been used synonymously.
(O) Leary - Ó Laoghaire. (Laoghaire was one of the best-known personal names of Ancient Ireland). A sept of the Corca Laoidhe established in Muskerry, of importance in all fields of national activity, especially in literature, and in the military sphere both at home and as the Wild Geese.
(O) Lemon - Lenna Ó Leannáin (possibly from leann, a cloak or mantle; leanán, paramour, has also been suggested). This is the name of several distinct septs located respectively in Co.s Cork, Fermanagh, and Galway. The last named is of the Sodhan pre-Gaelic stock. The Fermanagh family were erenaghs of Lisgoole. Ó Leannáin is also used as a synonym of Lineen (Ó Luinín), another Fermanagh erenagh family. Further confusion arises from the fact that these have been widely changed to the English name Leonard.