Irish Names
This essay is the same on the pages of all 1 country that use the tradition, and what differs between them, their registers and their rankings, is on those pages.
Irish (Gaeilge, ISO 639 ga) is a Goidelic (Q-Celtic) language of the Insular Celtic branch, written in the Latin script. It is the first official language of the Republic of Ireland and is spoken natively in the Gaeltacht regions, with roughly 70,000–80,000 daily speakers and over a million with some competence; most Irish people today bear anglicised forms of Gaelic names while speaking English. The native naming system and its anglicised counterpart coexist, and the Irish-language form is often the legally and culturally "true" form behind an English spelling.
Seán Ó Dónaill
- Seán
- Part — Seán
- given name
- Role — given name
A worked example from the naming-practices survey; hover or tap a part to see its role.
Structure & order
A formal Irish name is [GIVEN] [SURNAME], e.g. Seán Ó Dónaill. The surname is a patronymic phrase: a prefix (Ó "descendant" or Mac "son") followed by an ancestor's name in the genitive case. Distinguishing epithets Óg ("young", ≈ Jr.) and Mór ("big"/"elder", ≈ Sr.) sit between the given name and surname: Seán Óg Ó Súilleabháin.
`` [GIVEN] ([ÓG/MÓR epithet]) [PREFIX] [ANCESTOR-name in genitive, lenited if feminine] ``
Given names
Irish given names come from several layers: native Gaelic names (Niamh, Tadhg, Gráinne), Christian/saints' and Biblical names adapted into Irish (Seán < John, Pól < Paul, Síle < Cecilia), and Norse/Norman borrowings (Siúrtán < Jordan). Gender is lexical rather than suffix-marked, though many names are clearly masculine or feminine by tradition. During the late-19th/20th-century Gaelic Revival, dormant names were brought back and some were newly coined, notably Saoirse ("freedom/liberty", popular from the 1920s independence era) and Aisling ("dream, vision"). Aoife (from aoibh, "beauty, radiance") is an old name that surged again in modern usage. Spellings like Siobhán, Saoirse, Tadhg and Caoimhe preserve Irish orthography and are routinely mispronounced by outsiders.
Family names & patronymics
Surnames are formed from two productive prefixes plus a genitive ancestor name:
- Ó (older Ua) = "descendant of" → Ó Dónaill "descendant of Dónall".
- Mac = "son of" → Mac Siúrtáin "son of Jordan". Variant Mag appears before a vowel or silent ⟨fh⟩ + vowel.
The prefixes inflect for the bearer's gender and marital status, and the following ancestor name takes lenition (séimhiú), an h inserted after the first consonant, in the feminine/married forms:
| Bearer | From Ó | From Mac | Meaning |
|---|---|---|---|
| Man | Ó (Dónaill) | Mac (Siúrtáin) | descendant / son of |
| Unmarried woman | Ní Dhónaill | Nic Shiúrtáin | "daughter of…" (< Iníon Uí / Iníon Mhic) |
| Married woman (husband's name) | (Bean) Uí | (Bean) Mhic | "wife of a descendant / of a son" |
Uí is the genitive/plural of Ó and also denotes a whole kin-group, Uí Néill = "the descendants/clan of Niall". The female forms Ní, Nic, Uí, Mhic all lenite the following name, except that Nic (and Mac) do not lenite a name beginning with ⟨c⟩ or ⟨g⟩ (so Nic Gearailt, not Nic Ghearailt). Surnames are inherited patrilineally; the gendered prefix is re-derived for each bearer rather than passed verbatim.
How to address someone
In English, standard titles apply (Mr / Mrs / Ms / Dr + surname). In Irish, the surname prefix already encodes gender, so a woman is named with Ní/Nic regardless of title. The honorific A (vocative particle) plus lenition is used in address and letters (A Sheáin = "Dear Seán"). Religious and clan-historical contexts may use Ó lineage names directly (e.g. Ó Néill as a dynastic title).
Pitfalls for software
- Gendered surnames break naive matching. Ó Súilleabháin, Ní Shúilleabháin and Uí Shúilleabháin are the same family name for a man, his unmarried daughter, and his wife; string-equality and family clustering must normalise the prefix and undo lenition.
- Lenition mutates the spelling, so Dónaill → Dhónaill, Siúrtáin → Shiúrtáin. A parser must strip the inserted h to recover the root surname, while respecting the ⟨c⟩/⟨g⟩-after-Nic exception.
- Anglicisation is lossy and inconsistent. Ó/Mac may become O', Mc, Mac, or vanish (Ó Súilleabháin → Sullivan). Mc vs Mac carries no reliable Irish-vs-Scottish or religious signal despite folk belief.
- Genitive case means the ancestor name in the surname differs from its nominative citation form (Dónall → Dónaill), which can confuse lookups that expect the base name.
- Óg/Mór epithets sit mid-name and are not part of the surname; treating them as middle names or surname tokens is wrong.
All worked examples
| Full name | Part | Role |
|---|---|---|
| Seán Ó Dónaill | Seán | given name |
| Ó Dónaill | surname: Ó "descendant" + Dónall (genitive Dónaill) | |
| Aoife Ní Dhónaill | Aoife | given name (revival/native) |
| Ní Dhónaill | feminine surname: Ní "daughter" + lenited Dhónaill | |
| Pádraig Mac Lochlainn | Mac Lochlainn | Mac "son" + genitive Lochlainn |
| Saoirse Nic Lochlainn | Nic Lochlainn | feminine: Nic; no lenition (begins with ⟨L⟩… here lenited L→ none shown) |
| John O'Donnell (anglicised) | O'Donnell | Ó Dónaill with ⟨O'⟩ apostrophe retained |
| John Donnelly / Sullivan | Donnelly/Sullivan | anglicised form that drops the Ó/Mac prefix entirely |
See also
British Names · Patronymics and Lineage · Gender Marking · Surname Formation · Name Ordering
Where these names are used
The commonest given names and surnames of each, from its official register where one exists.
Cite this page: Mondonomo, “Irish Names”, https://mondonomo.ai/names/tradition/irish.