Irish surname

A formal Irish-language personal name consists of a given name and a surname. Surnames in Irish are generally patronymic in etymology, although they are no longer literal patronyms, as Icelandic names are. The form of a surname varies according to whether its bearer is male or female, and in the case of a married woman, whether she chooses to adopt her husband's surname.

An alternative traditional naming convention consists of the first name followed by a double patronym, usually with the father and grandfather's names. This convention is not used for official purposes but is generalized in Gaeltachtaí or Irish-speaking areas, and also survives in some rural non-Gaeltacht areas. Sometimes the name of the mother or grandmother may be used instead of that of the father or grandfather.

A first name may be modified by an adjective to distinguish its bearer from other people with the same name. Mór ("big") and Óg ("young") are used to distinguish father and son, like English junior and senior, but are placed between the given name and the surname: Seán Óg Ó Súilleabháin corresponds to "John O'Sullivan Jr." (although anglicised versions of the name often drop the "O'" from the name).

The word Beag/Beg, meaning "little", can be used in place of Óg. This did not necessarily indicate that the younger person was small in stature, merely younger than his father. Sometimes beag would be used to imply a baby was small at birth, possibly premature.

Adjectives denoting hair colour may also be used, especially informally: Pádraig Rua ("red-haired Patrick"), Máire Bhán ("fair-haired Mary").

A male's surname generally takes the form Ó/Ua (meaning "descendant") or Mac ("son") followed by the genitive case of a name, as in Ó Dónaill ("descendant of Dónall") or Mac Lochlainn ("son of Lochlann").

A son has the same surname as his father. A female's surname replaces Ó with Ní (reduced from Iníon Uí - "daughter of descendant of") and Mac with Nic (reduced from Iníon Mhic - "daughter of the son of"); in both cases the following name undergoes lenition. However, if the second part of the surname begins with the letter C or G, it is not lenited after Nic. Thus the daughter of a man named Ó Dónaill has the surname Ní Dhónaill; the daughter of a man named Mac Lochlainn has the surname Nic Lochlainn. When anglicised, the name can remain O' or Mac, regardless of gender.

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