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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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57 thoughts on “Irish Gaelic Surnames”

  1. Hi, my surname is pronounced in old Irish Mac-Ka-van-nyeh but also down the same blood line Mac-ka-V-nah. Its spelt in English McAvany/McAvena, but pronounced in old irish. My dad says the original pronunciation
    is Mac-ka-V-nah. What would be the old irish spelling?

  2. Haigh Siobhan, Tá ceist agam.

    I was married recently and have always had my name as gaeilge I used to have a Ní in my name, my husbands surname is, as the article says, a non-irish name that took on irish phonetically, béataigh, do i just leave it simply, (my name) Béataigh or (my name) Uí Béataigh.

    1. A Aisling, a chara,

      Comhghairdeachas! As your husband’s name does not have Ó or Mac before it, I would see no reason to now add Uí or any other such form before it. I am not completely certain if Béataigh should have a séimhiú/lenition, however. I cannot find examples of the female forms of Béataigh in any surname databases I am aware of. Another surname that doesn’t have any Ó or Mac is Breatnach (Walsh) and when it’s a woman’s name, it takes a séimhiú and becomes Bhreatnach. I am, however, unsure if this is how Béataigh is.

      Sorry that I could not be of more help!


  3. Hi Siobhan, I have found your articles and advice really informative.

    I have looked and haven’t been able to find anything to answer this question – how do you deal with a surname for someone who is gender neutral? Assigning “son of” or “daughter of” wouldn’t be appropriate for them, and I have no idea what to do. What would you advise?

  4. dia duit! my surname is keenan and i was wondering would it be ní cianáin or ní chianáin as gaeilge?
    go raibh mile!!

  5. Kevin McKnight

    My last name is McKnight, but in Gaelic it is MacanRidire. How do I pronounce it.
    I know my first name is Caoimhin, pronounced Quevin, Anglo is Kevin.

  6. Día dúit ! My surname in english is carthy but all the irish translations on google are for mc carthy. Would they be considered the same translation in irish or is there a different translation for carthy if so what is it? Thank you!!!

  7. Dia duit! I stumbled upon this blog post after some (failed) Googling so I hope that I’m not bothering you all. I see that some last names gain a h when on a woman, such as Ó Murchú vs Ní Mhurchú. What is the rule for this? I know that a h is added before the last name when it starts with a vowel, such as Ó hAodha, but I’m not sure why some female last names have the h after the first letter and some don’t.

    Go raibh maith agat!

    1. Dia is Muire duit, a Chianáin!

      A h is added after the first consonant (this is called lenition/séimhiú) when Ní, Nic, Uí or Mhic is placed before the surname. Examples of the female versions of the surnames Ó Murchú and Mac Cárthaigh are Ní Mhurchú, Nic Chárthaigh, Uí Mhurchú, Mhic Chárthaigh. Ní and Nic denote a single woman/daughter. Uí and Mhic are for married women (eg. wife of Ó Murchú/Mac Cárthaigh). Uí and Mhic are also used to denote a possession of someone eg. carr Uí Mhurchú – Ó Murchú’s car.

      The h at the very beginning of a name/word is a different thing to lenition/séimhiú. This h is called h prothesis. Its usual purpose is to make a word/phrase easier and more pleasant to pronounce. It is usually used when one word ends in a vowel and the next begins with a vowel. Ó hAodha has a pleasanter sound than Ó Aodha. Ní hAodha and Uí hAodha are the female versions of this surname.

      Hope that helps!

  8. William Maserjian

    Dia Duit Siobha’n!!
    Any thoughts on the phonetic pronunciation of O’ Maoilmheana (Mulvey)?

    Go raibh maith agat!
    Bill Maserjian

  9. Barbara Quirke Scanlon

    Hi Siobhain, My surname is Quirke or Ní Chuirc as gaelige. I have also seen it spelĺed as Quirk. Would you know are both spellings correct and what is the origin please.
    Many thanks

  10. Hi,
    My surname is Greene and is not of English origin. I was wondering if you could help me with finding out what my surname would be in its correct original Irish form. I have found variations such as Ó hUainín, Ó hUaithnín, Ó hUaine, MacGlaisín, Ó hUaithne, Ó hUaithnigh, however unsure as to which is the correct one.

    Thank you.

    1. A chara,

      They are all forms of the English surname Green, so unfortunately unless you know which version your family would have used there is no way for me to tell which one is correct. It may help for you to identify the parts of Ireland each one of these come from and from there identify which is the most likely version your family used.

      Le beannacht,