(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.
Mac Loughlin - Mac Lochlainn (from a Norse personal name): Of Inishowen. A senior branch of the Northern Uí Néill. They lost their early importance as a leading sept of Tirconnell in the thirteenth century, but are still very numerous in their original homeland-Co.s Donegal and Derry-where their name is usually spelt MacLaughlin; MacLoughlin, also numerous, is more widespread. Minor septs in Connacht were akin to the MacDermota and the O’Connors.
Mac Mahon - Mac Mathghamhna mod. Mac Mathúna (mathghamhan, bear): Thename of two septs, both of importance. That of Thomond descends from Mahon O’Brien, grandson of Brian Ború. MacMahon is now the most numerous name in Co. Clare. In later times the majority of the many of the name were from the Co. Monaghan, where McMahons are numerous today, though less so in Thomond.
(O) Malley - Mailey Ó Máille. (meall, peasant): A branch of the Cenél Eoghain located in Tyrone where their territory was known as ‘O’Mellan’s Country’. They were hereditary keepers of the Bell of St. Patrick.
O’Meara - Mara Ó Meadhra (meadhar, merry): This well-known sept, which has produced many distinguished men and women, gave its name to the village of Toomevara, which locates their homeland. This one of the few O names from which the prefix was never very widely dropped.
Molloy - Mulloy Ó Maolmmhuaidh. (The adjective muadh): denotes bit and soft as well noble). An important sept of Fercal in mid-Leister. Molly is an anglicized form of Ó Maolaoidh. Apart from five variant spellings, such as Maloy and Mulloy, Molloy has been officially recorded as synonym of Mulvogue (Connacht), Logue (Co. Donegal), Mullock (Offaly), Mulvihill (Kerry), and Slowey (Co. Monaghan) while Maloy has been used for MacCloy in Co. Derry.
(O) Moran: Apart from MacMorran of Fermanagh, which has inevitably been changed to Moran, there are a number of distinct septs of Ó Moráin and Ó Moghrain whose name is anglicized Moran. Four of these are of Connacht-in which province the name is much more numerous than elsewhere-originally located (a) at Elphin (akin to the O’Connors), (b) in Co. Leitrim (of the Muinitir Eolais), (c) in. Co. Mayo at Ardanee, (d) in Co. Galway, a minor branch of the Uí Maine. The Leitrim families are also called Morahan, as is the fifth to be enumerated, viz. that of Offaly, where Morrin is a synonym.
Moynihan - Ó Muimhneacháin (Muimhneach, Munsterman): Although there was a small sept of this name, sometimes changed to Munster, in Mayo, families so called belong almost exclusively to south-west Munster, Moynihan being very numerous on the borders of two counties. Minihan, another form of the name, is mainly found in Cork.
(O) Mulligan - Ó Maolagáin (probably a diminutive of maol, see MacMullen): An important sept in Donegal, much reduced at the time of the Plantation of Ulster and now found more in Co. Mayo and Monaghan.
(O) Murphy - Ó Murchadh: Murphy is the most numerous name in Ireland. The resumption of the prefixes O and Mac, which is a modern tendency with most Gaelic-Irish names, has not taken place in the case of Murphy.
(Mac) Nally - Mac Anally Mac an Fhailghih (failgheach, poor man): Without the prefix Mac this name now is found mainly in Mayo and Roscommon; with the Mac it belongs to Oriel. Woulfe says that the Mayo Nallys are of Norman or Welsh oigin and acquired a Gaelic name. This is unlikely in the case of the MacNallys of Ulster as there they are often called Mac Con Ulaidh (son of the hound of Ulidia, i.e. eastern Ulster). In the ‘census ‘ of 1659 it appears as MacAnully, MacEnolly, MacNally, and Knally, all in Oriel or in counties adjacent thereto.
Mac Namara - Mac Conmara (hound of the sea): The most important sept of the Dál gCais after the O’Briens to whom they were marshals.