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Many Irish surnames were changed upon immigration to a new country. Others may have been altered with the passing of generations and many of our ancestors might have had close relations, with surnames slightly different to their own. Understanding your Irish surname, its different components, and variations can help you widen or narrow your genealogical search for clues to your ancestors' origins.

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Irish naming conventions

Surnames in Irish are generally patronymic i.e. they are based on the given name of the father. For example, the common Irish name Ó Murchú which is known as Murphy in English literally means ‘Son of or descendant of Murchú (a personal name)’.

Irish Male Last Names

A male surname generally takes the form of “Ó” (descendent of) or “Mac” (son of) followed by the genitive case of the name i.e. Seán Ó Súilleabháin (Seán descendant of Súilleabhán) anglicised as John O’Sullivan, or Pádraig Ó Dochartaigh (Pádraig descendent of Dochartach) anglicised as Patrick Doherty. The adjectives ‘mór’ (big) and ‘óg’ (young) can also be added into male surnames to distinguish between father and son, similar to ‘junior’ and ‘senior’ in English i.e. Seán Mór Ó Súilleabháin (father) and Seán Óg Ó Súilleabháin (son). Sometimes even hair colour can be used within a name i.e. Pádraig Rua Ó Dochartaigh (rua meaning red-haired).

Irish Female Last Names

Female surnames are slightly different; instead of Ó a female surname uses (a contraction of Iníon (daughter of descendent of), and instead of Mac a female surname uses Nic (a contraction of Iníon mhic (daughter of the son of). In both cases the following name undergoes lenition in certain consonants, which means that the letter h is added in after the first letter of the name i.e. Ó Dónaill (O’Donnell male surname) Ní Dhónaill (O’Donnell female surname), or Mac Pháidín (McFadden male surname), Nic Pháidín (McFadden female surname). If a woman marries and chooses to take her spouse’s surname Ó becomes Bean Uí (wife of descendent of) or simply and Mac changes to Bean Mhic or simply Mhic i.e. Máire (Bean) Uí Dhónaill, Sorcha (Bean) Mhic Pháidín. Note that the second name lenites in the feminine form (a h is added) except for some exception cases i.e. after C or G.

If the surname begins with a vowel Eára, Uiginn, a lower case h is added after Ó i.e. Ó hEára, Ó hUiginn but the feminine forms effect no change i.e. Ní Eára, Uí Eára, Ní Uiginn, Uí Uiginn. 

Male Meaning Anglicised Daughter Wife
Mac Son of Mc, Mac, Mag Nic Mhic
Ó Descendant of O'

Online Resources

There are some excellent online resources for those keen to find out more about Irish names. 

Library Ireland

Library Ireland has some excellent online resources for researching Irish names.

Gaois - Irish-language surnames database

Dublin City University has provided a useful online resource called Gaois. This is a linguistic database of Irish-language surnames and provides in-depth lexical and grammatical information regarding a selection of high-frequency surnames of Irish-language origin. Irish-language surnames in the database are arranged in clusters which contain their synonyms in Irish and their equivalents in English. Inflected forms of the Irish-language surnames are also given. The database currently comprises nearly 700 surname clusters and details the male, wife and daughter forms of names along with historical versions of names:

Irish Identity – Irish/English Name Index

The Irish Identity website ( contains lists of Irish first names and surnames, searchable by the letter the name begins with. A very straightforward and user friendly resource. is a useful tool for those who may wish to hear the pronunciation of a word or term in Irish. It is a voice synthesizer can offer an approximate pronunciation of words and phrases in the major dialects of modern Irish. While no tool of this nature is a substitute for having a human speaker of the language to advise on pronunciation, it does offer those who don’t speak Irish a good place to start. 

Useful Reference Books

‘The Surnames of Ireland’ by Edward MacLysaght

Edward MacLysaght was a leading authority on Irish names and family history. He served as Chief Herald and Genealogical Officer of the Irish Office of Arms. He was also Keeper of Manuscripts of the National Library of Ireland and was Chairman of the Manuscripts Commission. His book, ‘The Surnames of Ireland’ is considered one of the most valuable resources for researching Irish names. (Publisher: Irish Academic Press Ltd), ISBN-10: ‎ 0716523663, ISBN-13: ‎978-0716523666

‘An Sloinnteoir Gaeilge agus an tAinmneoir’ by Muiris Ó Droighneáin

This small but informative book is published by Coiscéim and allows the reader to look up surnames in English to find out the Gaelic/Irish version of the name before it became anglicised. It also includes first names and is widely available from bookshops and online sellers.

Library Ireland also includes a link to numerous books about Irish Names:

Thanks to Pól Ó Frighil of Derry City & Strabane District Council and our Volunteer Partner colleagues at the Tower Museum for providing this article.

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