100 Irish Surnames and Their Meanings
Ó does not mean "of". It means grandson or descendant of, and Mac means son of — two different generational claims, not two spellings of the same idea. The reason this matters is what happened next: under English rule the prefixes were widely dropped, so a family recorded as Ó Súilleabháin in Irish sources appears as Sullivan in the 1800s and O'Sullivan again after the Gaelic revival. Same family, three surnames, no adoption and no marriage involved. Ireland also carries a Norman layer (the Fitz- names) that has been Irish for eight hundred years. If a name has put cousins on both sides of an ocean, the cousin calculator will sort out what they are to each other.
What does your Irish surname start with? Tap the closest match.
Tap an option above. The prefix tells you the naming system; the root tells you the ancestor.
What Ó and Mac actually mean
Two prefixes carry most of the Gaelic surname stock, and they are not interchangeable.
Ó (older spelling Ua) means "grandson of" or, more loosely, "descendant of". It was fixed to a named ancestor and then frozen. Ó Briain means descendant of Brian — specifically Brian Bóruma, who died in 1014, which is why the O'Brien name can be dated so precisely.
Mac means "son of". Mac Cárthaigh is son of Cárthach. In practice both prefixes became hereditary at roughly the same period, between about 950 and 1150, which makes Ireland's surname system one of the oldest in Europe.
Mc is not a separate thing. It is a contraction of Mac used by scribes and printers to save space, and the same family shows up as MacMahon and McMahon across a single parish register. The idea that Mc is Irish and Mac is Scottish is a myth, as is the idea that one is Catholic and one Protestant.
The apostrophe in O'Brien is an English invention. In Irish it is Ó with a fada, an accent that lengthens the vowel. English printers read the accent as a mark of elision and set an apostrophe, and it stuck.
Ní and Nic are the female forms. A daughter of an Ó Súilleabháin man was Ní Shúilleabháin, not Ó Súilleabháin, and a daughter of a Mac man was Nic. Irish records written in Irish use these, which occasionally confuses researchers who expect a woman to carry her father's exact name. The wider pattern of naming children after fathers is covered in patronymic surnames.
Maol and Giolla mean "devotee" or "servant". Ó Maoil Eoin (Malone) is descendant of the servant of St John; Mac Giolla Phádraig (Fitzpatrick) is son of the devotee of St Patrick. These are religious names in disguise, and they are a distinctly Irish and Scottish habit shared with the wider stock of Celtic surnames.
Why the same family is O'Sullivan and Sullivan
The single biggest source of confusion in Irish family history, and it is entirely a political story.
The prefixes were stripped from the 1600s onward. Under English administration, in a legal and commercial world conducted in English, the Ó and Mac were dropped — sometimes by clerks, sometimes deliberately by families who found a plain name easier to live with.
By the 1800s most bearers had no prefix. Griffith's Valuation and the civil registers are full of Sullivan, Brien, Connor, Donnell and Carthy with the prefix gone.
The Gaelic revival put many of them back. From the 1890s onward, and with real momentum after independence, families re-adopted O' and Mac. This is why a grandfather can be Sullivan on his marriage certificate and O'Sullivan on his headstone.
Re-adoption was not always accurate. Some families restored a prefix their line had never used, and a few restored the wrong one — an Ó name coming back as Mac. Treat a modern prefix as a claim, not as evidence.
Search both forms, always. When you work through the free sources described in Irish genealogy records, run every search with and without the prefix, and with Mac, Mc and M' as separate spellings.
The practical rule: the prefix is the least stable part of an Irish surname. The root is what identifies the family.
The Norman layer and the Old English families
Not every Irish surname is Gaelic, and some of the most Irish-sounding ones are not.
The Anglo-Norman invasion of 1169 brought a second naming system. Fitz- comes from Old French fils, "son", so Fitzgerald is son of Gerald and Fitzsimons son of Simon, formed exactly like Mac names but in a different language.
These families were assimilated within a few generations. The Burkes, Fitzgeralds and Barrys spoke Irish, married Irish, patronised Irish poets and were described, in a phrase that has outlived its source, as more Irish than the Irish themselves. Some even took Gaelic-style names: the de Angulo family became Mac Oisdealbhaigh, anglicised as Costello, the first Norman family to adopt a Mac name.
"Old English" is the historians' term for them, distinguishing the medieval Norman settlers from the "New English" of the Tudor and Stuart plantations. A Burke or a Roche in a seventeenth-century record is usually Old English and usually Catholic.
Fitzpatrick runs the other way. It is not Norman at all — it is Mac Giolla Phádraig, a Gaelic name of the Osraige kings dressed in Norman clothing by translation.
Plantation surnames are a later, separate layer. English and Scottish names in Ulster from the 1600s — Armstrong, Johnston, Elliott, Bell — are a different story again, and overlap heavily with Scottish surnames.
Ó names: descendant of
Roughly thirty of the most common. The prefix is shown as it is usually written today; the same names appear constantly without it.
| Surname | Meaning or origin |
|---|---|
| O'Sullivan (Ó Súilleabháin) | Descendant of Súilleabhán, from súil "eye"; the second element is disputed, with "one-eyed" and "hawk-eyed" both proposed |
| O'Brien (Ó Briain) | Descendant of Brian Bóruma, died 1014; the name Brian is usually read as "noble" or "high" |
| O'Neill (Ó Néill) | Descendant of Niall; the personal name is old and its meaning uncertain, often glossed "champion" |
| O'Connor (Ó Conchobhair) | Descendant of Conchobhar, an old name combining "hound" or "wolf" with "desire" |
| O'Donnell (Ó Dónaill) | Descendant of Domhnall, "world-mighty", from domhan "world" and a root meaning "rule" |
| Kelly (Ó Ceallaigh) | Descendant of Ceallach; the meaning is genuinely disputed — "bright-headed", "strife" and a link to ceall "church" are all argued |
| Murphy (Ó Murchadha) | Descendant of Murchadh, "sea warrior", from muir "sea" and cath "battle" |
| Ryan (Ó Riain) | Descendant of Rian, most often linked to rí "king"; some Ryans are instead Ó Maoilriain |
| Byrne (Ó Broin) | Descendant of Bran, "raven" |
| Doherty (Ó Dochartaigh) | Descendant of Dochartach, "obstructive" or "hurtful" |
| Gallagher (Ó Gallchobhair) | Descendant of Gallchobhar, "foreign help", gall plus cobhair |
| Kennedy (Ó Cinnéide) | From ceann "head" and éidigh "ugly, grim" — a blunt descriptive nickname turned dynastic name |
| Flaherty (Ó Flaithbheartaigh) | Descendant of Flaithbheartach, "generous prince" or "bright ruler" |
| Casey (Ó Cathasaigh) | Descendant of Cathasach, "vigilant, watchful" |
| Whelan / Phelan (Ó Faoláin) | Descendant of Faolán, a diminutive of faol "wolf" |
| Mahony (Ó Mathghamhna) | Descendant of Mathghamhain, "bear" |
| Daly (Ó Dálaigh) | Descendant of Dálach, from dáil "assembly" — the great bardic family |
| Farrell (Ó Fearghail) | Descendant of Fearghal, "man of valour", fear plus gal |
| O'Toole (Ó Tuathail) | Descendant of Tuathal, "ruler of the people" |
| O'Connell (Ó Conaill) | Descendant of Conall, joining "hound" or "wolf" with a root meaning strength |
| Donoghue (Ó Donnchadha) | Descendant of Donnchadh, "brown warrior", donn plus cath |
| Riordan (Ó Ríordáin) | Descendant of Ríoghbhardán, "royal bard" |
| Hogan (Ó hÓgáin) | Descendant of Ógán, from óg "young" |
| Quinn (Ó Cuinn) | Descendant of Conn, an old name meaning "chief" or "sense, intelligence" |
| Dwyer (Ó Duibhir) | From dubh "black" and odhar "dun, sallow" |
| Nolan (Ó Nualláin) | Descendant of Nuallán, from nuall "famous" or "shout" |
| Moriarty (Ó Muircheartaigh) | "Sea navigator", from muir "sea" and ceartach "skilled, directing" |
| Tierney (Ó Tighearnaigh) | From tighearna, "lord" |
| Cronin (Ó Cróinín) | From crón, "swarthy" or "dark yellow" |
| Treacy (Ó Treasaigh) | From treasach, "warlike" |
Mac names: son of
| Surname | Meaning or origin |
|---|---|
| McCarthy (Mac Cárthaigh) | Son of Cárthach, "loving" — the great Desmond ruling family |
| McMahon (Mac Mathúna) | Son of Mathghamhain, "bear" |
| McDermott (Mac Diarmada) | Son of Diarmaid; the old gloss "without envy" is folk etymology and the true meaning is uncertain |
| McGowan (Mac Gabhann) | Son of the smith — frequently translated outright into Smith |
| MacNamara (Mac Con Mara) | Son of Cú Mara, "hound of the sea" |
| Maguire (Mac Uidhir) | Son of Odhar, "dun-colored, sallow" |
| McGrath (Mac Craith) | Son of Craith, from rath "grace, prosperity" |
| McHugh (Mac Aodha) | Son of Aodh, "fire" — the same root gives Hughes and Hayes |
| Sweeney (Mac Suibhne) | Son of Suibhne, "pleasant"; a gallowglass family of Scottish origin settled in Donegal |
| McLoughlin (Mac Lochlainn) | Son of Lochlann, a name meaning "Scandinavia" or "Viking" |
| MacAuliffe (Mac Amhlaoibh) | Son of Amhlaoibh, the Irish form of Norse Óláfr |
| Reynolds (Mac Raghnaill) | Son of Raghnall, from Norse Rögnvaldr — the English form was chosen for sound, not meaning |
| McGuinness (Mac Aonghusa) | Son of Aonghus, "one choice" or "one vigor" |
| McCann (Mac Cana) | Son of Cana, usually read as "wolf cub" |
| Clancy (Mac Fhlannchadha) | Son of Flannchadh, "red warrior", flann plus cath |
| MacIntyre / McAteer (Mac an tSaoir) | Son of the craftsman or carpenter |
| Ward (Mac an Bhaird) | Son of the bard; a hereditary poetic family. English Wards are unrelated, from "warden" |
| McBride (Mac Giolla Bhríde) | Son of the devotee of St Brigid |
| Egan (Mac Aodhagáin) | Son of Aodhagán, a double diminutive of Aodh "fire" |
| Keogh (Mac Eochaidh) | Son of Eochaidh, from each "horse" |
| McKeon / McKeown (Mac Eoin) | Son of Eoin, the Irish form of John |
| MacNeill (Mac Néill) | Son of Niall — the Mac counterpart of O'Neill |
| McCormack (Mac Cormaic) | Son of Cormac; the elements are old and the meaning is debated |
| Costello (Mac Oisdealbhaigh) | Son of Oisdealbhach — a Norman family, de Angulo, that adopted a Gaelic Mac name |
Norman-Irish and Old English names
| Surname | Meaning or origin |
|---|---|
| Fitzgerald | Anglo-Norman "son of Gerald", from French fils |
| Fitzpatrick | Not Norman: a translation of Mac Giolla Phádraig, "son of the devotee of Patrick" |
| Fitzmaurice | "Son of Maurice", a Desmond Geraldine branch |
| Fitzgibbon | "Son of Gibbon", a pet form of Gilbert |
| Fitzsimons | "Son of Simon" |
| Burke / de Burgh | From the Norman family de Burgo, whose name means "of the fortified town" |
| Barry | From the Norman de Barri, taken from a place name — Barry Island in Wales is the usual candidate |
| Roche | From French roche, "rock" — originally de la Roche |
| Power | From le Poer; usually read as Old French "the poor", though a Picard place name is also proposed |
| Walsh (Breathnach) | "The Briton" — a name given to Welsh and Cambro-Norman settlers |
| Butler | From le Botiller, the hereditary Chief Butler of Ireland; the Ormond family |
| Nugent | From Nogent in France |
| Dillon | Norman, from a personal name of Germanic origin |
| Prendergast | From a place in Pembrokeshire |
| Lacy / de Lacy | From Lassy in Normandy |
| Cusack | From Cussac in France |
| Plunkett | Norman, plausibly from blanchet, a term for white cloth |
| Purcell | From Old French pourcel, "piglet" — a swineherd or a nickname |
| Talbot | Norman, from a Germanic personal name |
| Bermingham | From Birmingham in England |
| Fleming | "The Fleming" — a settler from Flanders |
| Joyce | From Breton Iodoc, a saint's name that also gives Josse and Jocelyn |
| Tyrrell | Norman, from a nickname often read as "stubborn" |
| Dalton | From an English place name meaning "valley settlement" |
| Wall (de Valle) | "Of the valley", later confused with English Wall |
| Devereux | From Évreux in Normandy |
Gaelic names without a prefix, color names and Norse names
| Surname | Meaning or origin |
|---|---|
| Doyle (Ó Dubhghaill) | "Dark foreigner" — the Irish term for Danes, so a Norse-descended line |
| Higgins (Ó hUiginn) | Usually from uiginn, "Viking, sea-rover"; a separate English Higgins exists from Hick, a pet form of Richard |
| Kavanagh (Caomhánach) | "Follower of St Caomhán" — one of the rare Irish surnames that never took Ó or Mac |
| Kinsella (Cinnsealach) | Another prefix-free Leinster name, from the same royal line as Kavanagh |
| Duff (Dubh) | "Black", usually of hair |
| Bane / Bawn (Bán) | "White, fair" |
| Malone (Ó Maoil Eoin) | "Devotee of St John" |
| Mulligan (Ó Maolagáin) | From maol, "bald" or "tonsured" — a follower of the church |
| Muldoon (Ó Maoldúin) | "Chief of the fort", from maol and dún |
| Mulcahy (Ó Maolchathaigh) | "Devotee of Cathach" |
| Delaney (Ó Dubhshláine) | "Black of the Slaney", carrying a river name |
| Sheridan (Ó Sirideáin) | Descendant of Sirideán, a personal name of uncertain meaning |
| Rafferty (Ó Rabhartaigh) | From rabhartach, "prosperous" or "spring tide" |
| Cassidy (Ó Caiside) | Usually from cas, "curly-haired" |
| Halloran (Ó hAllmhuráin) | From allmhurach, "from overseas, stranger" |
| Hennessy (Ó hAonghusa) | Descendant of Aonghus, "one choice" |
| Lawlor (Ó Leathlobhair) | "Half-sick" or "half-leper", a stark descriptive name |
| Fallon (Ó Fallamháin) | From follamhnas, "leadership, rule" |
| Scanlon (Ó Scannláin) | From scannal, "contention" |
| Naughton (Ó Neachtain) | Descendant of Neachtan, an ancient name usually linked to a root meaning "clean, pure" |
| Quigley (Ó Coigligh) | From coigeal, "untidy or dishevelled hair" |
| Coughlan (Ó Cochláin) | From cochall, "cape, hood" |
| Reilly (Ó Raghallaigh) | Descendant of Raghallach; the personal name's meaning is not settled |
| Boyle (Ó Baoill) | Descendant of Baoll; meaning uncertain, and worth resisting the confident glosses you will see |
| Dowd (Ó Dubhda) | From dubh, "black" |
| Griffin (Ó Gríobhtha) | From gríobh, "griffin"; note that English and Welsh Griffins descend instead from Gruffudd |
| Collins (Ó Coileáin) | From coileán, "whelp, young hound"; many English Collinses are instead from Colin, a pet form of Nicholas |
| Lynch (Ó Loingsigh) | From long "ship", so "mariner" — but the Galway Lynches are Norman de Lench, a genuinely separate family |
| Gorman (Ó Gormáin) | From gorm, "blue" or "dark" |
| Shanahan (Ó Seanacháin) | From sean, "old" or "wise" |
Anglicisation, translation and the spelling problem
Irish surnames reached English records through people who mostly could not write Irish, and it shows.
Most anglicisations are phonetic. A clerk heard Ó Súilleabháin and wrote what it sounded like. Ó Dubhthaigh became Duffy, Ó hAodha became Hughes and also Hayes, Ó Séaghdha became Shea and O'Shea.
Some are translations, which is far more disruptive. Mac Gabhann means "son of the smith", so entire McGowan families simply became Smith. Ó Duibhinn was sometimes rendered Devine. A translated name shares no sound with its original at all, which is why it defeats every wildcard search you can build.
Some are mistranslations. A name containing a word that resembled another Irish word could be turned into an unrelated English name by a well-meaning clerk with poor Irish.
One Irish name can produce a dozen English spellings. Ó Maoilriain gives Ryan, Mulryan, O'Mulryan and Ryain. The general mechanics of this are worked through in surname spelling variations.
Different English names can collapse onto one Irish name, and vice versa. Hayes covers Ó hAodha in Munster and an English place-name surname in Britain. The name alone will not tell you which you have.
Emigration added another round. American and Australian clerks re-spelled Irish names again on arrival, and family members who emigrated in different decades sometimes ended up with permanently different surnames.
What an Irish surname can and cannot tell you
Useful, but far weaker evidence than most people assume.
It can suggest a region. Irish surnames are unusually well localised: O'Sullivan and McCarthy in Cork and Kerry, Doherty and Gallagher in Donegal, Maguire in Fermanagh, Kavanagh in Wexford and Carlow. Griffith's Valuation and the 1901 census let you map this yourself.
It cannot prove descent from a chief. Every Ó Néill is descended from someone in that kindred's orbit, but medieval Irish lordships absorbed followers, tenants and clients who took the ruling name. Sharing a surname with a king is not a lineage.
It cannot separate two unrelated families with the same name. There are several independent Ó Ceallaigh kindreds in different provinces, none descended from the others.
It cannot date your emigration or fix your religion. Both Catholic and Protestant families bear Gaelic names, and plantation-era English names are borne by Catholic families whose ancestors converted or intermarried.
DNA does the work a surname cannot. Y-DNA testing groups men who genuinely share a paternal line, whatever their name became — start from find your last name origin if you want the general approach.
Treat the name as a lead. It tells you where to look first, and nothing more than that.
No coat of arms belongs to an Irish surname
Worth being firm about, because the trade in "Irish family crests" is enormous.
Arms are granted to individuals, not to names. A grant made to one Murphy says nothing about the other several hundred thousand of them. There is no such thing as "the Murphy coat of arms".
The shield you can buy is somebody else's. Souvenir sellers match a surname to a real grant made to a real, unrelated family, and print it on a plaque. It is not yours.
Ireland has an actual heraldic authority, the Chief Herald of Ireland, which grants arms to people and bodies — and does not grant them to surnames.
Designing your own is the honest version, and it is a genuinely good project; there is a full walkthrough at make a family coat of arms.
FAQ
Is Mc Irish and Mac Scottish?
No. Mc is simply a written abbreviation of Mac, used by scribes and printers in both countries. The same Irish family appears as MacMahon and McMahon in different records, sometimes on the same page. There is also no Catholic or Protestant distinction between them.
Why do some Irish surnames have no O' or Mac?
Because the prefix was stripped during English rule, when official life ran in English. Murphy, Kelly, Ryan and Sullivan all originally carried Ó. Some families restored the prefix after the Gaelic revival from the 1890s, which is why one family can show both forms within living memory.
What is the most common Irish surname?
Murphy, from Ó Murchadha, "sea warrior". Kelly is second, then O'Sullivan, Walsh and Smith — Smith mostly representing translated Mac Gabhann families rather than English settlers, which is a good illustration of how misleading a raw surname count can be.
Are all Fitz- names Norman?
Almost all. Fitz comes from Old French fils, "son", and Fitzgerald, Fitzmaurice and Fitzsimons are Anglo-Norman families settled after 1169. Fitzpatrick is the exception: it is Mac Giolla Phádraig, a Gaelic name from the kings of Osraige, translated into Norman form.
Does my Irish surname mean I belong to a clan?
Not in the way clan merchandise implies. Irish kindreds absorbed followers, tenants and dependants who adopted the ruling family's name without sharing its bloodline, and several unrelated families used the same name in different provinces. The surname places you in a name group, not a proven lineage.
Where can I check where my surname was concentrated in Ireland?
Griffith's Valuation, the 1901 and 1911 censuses and the civil registration indexes all let you map a surname by county and even by townland, and all three are free. The route through them is set out in Irish genealogy records.
Reading an Irish name like a record
An Irish surname is a compressed piece of medieval documentation: a prefix that states a generational relationship, a root that names a specific man, and several centuries of political interference layered on top. Read it in that order. Strip the prefix before you search, because the records mostly did. Expect translation as well as respelling, so a McGowan line can genuinely become Smith. Use the county concentrations as a starting point rather than as proof, and let Y-DNA rather than the name settle questions of descent. Once the emigrant siblings and their descendants are on paper, the cousin calculator will tell you exactly what each of them is to you.
