Irish Gaelic Surnames

You’ve probably heard this little rhyme at one time or another:

By Mac and Ó you’ll always know true Irishmen they say. But if they lack the Ó and Mac, no Irishmen are they.

A cute rhyme, as far as it goes, but the reality is that Irish surnames are much, much more complicated than that — particularly surnames in Irish Gaelic.

In this post we’ll take a look at surnames in Irish…particularly at how “mac” and “ó” surnames came to be, and why many very Irish surnames either lack them now or never had them to begin with.

Gaelic Surnames: Source of “Mac” and “Ó”

Many of the Irish surnames with which you are familiar — Murphy, Sweeny, Ryan, etc. — come from the culture of the Gaels: The Celts  that populated Ireland (and ultimately Scotland and the Isle of Man).

Gaelic surnames are “patronymics,” that is, they indicate patrilineal descent. Originally they weren’t surnames at all, but just a way of distinguishing similarly named individuals:

“Do you know Tom?”

“Tom James’ son?”

“No…Tom John’s son.”

In English, this practice ultimately gave us such surnames as “Jameson” and “Johnson.” Much the same thing happened among the Gaels.

The Irish word for “son” — mac — would be placed in front of the person’s father’s given name, nickname, or occupation, which would be in the “genitive” or “possessive” case:

Eoghan Mac Suibhne – Eoghan Son of Suibhne.

A similar system existed for females, using nic — a form of the Irish word for “daughter”:

Gráinne Nic Mhurchú – Gráinne Daughter of Murchú.

What about the “Ó’s”?


The “Ó” surnames came along much later, as a result of people wanting to identify themselves as descendants of a famous ancestor. “Ó” means “grandson/male descendant”:

Colm Ó Riain – Colm Descendant of Rian.

As with mac, a similar system existed for females, using another form of the Irish word for “daughter”: ní.

Eibhlín Ní Riain – Eibhlín Daughter of Rian.

So where did “mac” and “ó” go?


Well, in Irish, they haven’t gone anywhere.  When people who have surnames of Gaelic origin write or say them in the Irish language, they use Mac, Ó, Nic, oras appropriate.

In English, it’s another story. As Gaelic names were Anglicized, sometimes they lost their prefixes:

Ó Suibhne became “Sweeny.”

Mac Murchú became “Murphy.”

Ó Riain became “Ryan.”

Some retained their prefixes, but in an altered form. For example, Mac became “Mc” or “Ma” and Ó became “O’.”

(By the way, there’s no truth to the old line about “Mc” indicating an Irish name and “Mac” indicating a Scottish name. In fact, both cultures use both prefixes).

To make things even more confusing, names weren’t Anglicized consistently…in fact, they were all over the map!

You might, for example, have one family called “Riley,” one called “Reilly” and another called “O’Reilly” or “O’Riley (all of which were originally Ó Raghallaigh).

Non-Gaelic Irish Surnames

Not all Irish surnames are of Gaelic origin, however. Over the centuries, Ireland has attracted people from various cultures, all of which have left their mark on the landscape of Irish surnames.

In fact, some of the best-known Irish surnames, such as Fitzgerald, Joyce, Walsh, Power, and Burke, come to us from the Normans.

The Normans may have come to Ireland as would-be conquerers, but they eventually became “more Irish than the Irish,” intermarrying with the Gaelic tribes and even adopting their language.

They adopted Gaelic forms of their surnames as well. Some who had names with the “fitz” prefix went with the mac form (“fitz” derives from “fils,” meaning “son” in French):

Mac Gearailt = Son of Gerald = Fitzgerald

Most, however, simply adopted a more Gaelic spelling and pronunciation for their Norman surnames:

Seoigh  (Anglicized as “Joyce”)

de Burca (Anglicized as “Burke”)

de Paor (Anglicized as “Power”)

Some had their surnames translated literally. For example, “Walsh” (a form of the word “Welsh”) became Breatnach: Irish for a Welsh person.

These names never sported a “Mac” or “Ó,” but are undeniably Irish!

The English and the Anglo-Irish


There’s little doubt that the English left their mark as well. In fact, the man that many consider the quintessential Irish poet, William Butler Yeats, had a surname that was of English origin.

“Yeats” is still quite a common surname in Ireland, as are other names of English origin, particularly occupational names, such as “Cooper,” “Baker,” and “Smith.”

Some of these names don’t have natural Irish language forms in and of themselves, at least not in the traditional Gaelic patronymic sense, though they can be “Gaelicized.”

Occupational names, or English names ending in “son” (such as “Williamson”) can easily be adapted to the “mac” form (you’ll see “Williamson” rendered as “Mac Liam,” for example).

In other cases, often the names are simply written in Irish phonetically, though sometimes the Norman “de” prefix will be added.

Generally speaking, any name that is associated with Ireland long enough will eventually acquire its own form in the Irish language, though it may or may not acquire a Gaelic prefix along the way.

So don’t despair “if you lack the Ó or Mac”!

Perhaps your name lost its prefix when it was Anglicized, or perhaps it never had one to begin with, but that doesn’t mean it’s any less Irish!

Did you find this article helpful?

Did you know all this about Irish surnames before? Let us know your thoughts below!

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14 thoughts on “Irish Gaelic Surnames”

  1. Hi my surname is Keoghane I’m told it’s irish and want to know the corect pronounciation I think a letter or two has been added over time , can anyone shed dome light on it ? Thanks

  2. According to, my name (Ledwith) was also spelled Ledwidge, but another source tells me it was from the Gaelic spelling, Leadus (with accents on the e and u). How would that spelling be pronounced? Does it sound a bit like Ledwidge, Ledwich or Ledwith? I am trying to trace my Irish roots, but the spelling changes make it quite difficult! Thanks.

    1. Hi Barbara,

      Thank you for your comment.

      According to Sloinnte Gaedheal is Gall which was published in 1923, De Léadús (the Gaelic version), Ledwith, Ledwidge and its other variations were all derived from the Norman surname de ledwith. You can find out more here:

      Unfortunately, many people used various different spellings of their name during their lifetime.

      If you’ve any other questions, don’t hesitate to ask.

      Le meas,

  3. I have a question about the famous Irish harper Turlough O’Carolan. I was told (perhaps incorrectly) that if you just call him by his last name, you say “Carolan” but if you use his first name as well, you include the O’: Turlough O’Carolan. Is there any truth to this? Thank you.

    1. Hi Sylvia,

      Thank you for your comment.

      From what I see of any English language writings about the famous Irish harper Turlough O’Carolan, he is indeed often just called Carolan when his first name is not mentioned.

      His name in Irish is Toirdhealbhach Ó Cearbhalláin. When his first name is not included, he is called either an Cearbhallánach or Ó Cearbhalláin.

      Le meas,

  4. Jessica Cullinan

    Hi there,

    My surname is Cullinan, but I’ve been informed this is descendent from Ó Cuileannáin. Is this correct and if so, how do I pronounce it correctly? Much thanks:)

    1. Hi Jessica,

      Thank you for your question.

      Ó Cuileannáin is indeed the Irish for Cullinan.

      Ó Cuileannáin is the man’s surname. Women’s surnames depend on their marital status. If Cullinan is your maiden name, it would be Ní Chuileanáin but if you’ve married a man with the surname Callinan, you would be Uí Chuileanáin.

      You can hear Ní Chuileanáin being pronounced in the Ulster accent in this song

      It could also be pronounced with the “á” being pronounced as like the English word “awe”. /Nee Khil-en-aw-in/

      There is also the placename Baile Uí Chuileannáin / Ballycullinan

      Le gach dea-ghuí, (Kind regards)

  5. Hi-my ancestors in the southern Connemara Islands are Joyce, Connelly, Bailly and Flaherty. Can you tell me how to pronounce these family names ?

  6. Hello
    My surname is Deery. In Irish it is O’Daighre. I’m not 100% on the pronunciation. My family pronounce it ‘o’dare’ but I’m pretty sure ‘gh’ in Irish is ‘y’ If I were to start using the Irish form, as a female would it be Ni Daighre, or is it better to just stick with O’Daighre?

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