Irish Name - Surnames and Prefixes

Surnames and Prefixes

A male's surname generally takes the form Ó/Ua (originally "grandson") or Mac ("son") followed by the genitive case of a name, as in Ó Dónaill ("grandson of Dónall") or Mac Gearailt ("son of Gerald").

A son has the same surname as his father. A female's surname replaces Ó with Ní (reduced from Iníon Uí - "daughter of the grandson 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 and the daughter of a man named Mac Gearailt has the surname Nic Gearailt. When anglicised, the name can remain O' or Mac, regardless of gender.

If a woman marries, she may choose to take her husband's surname. In this case, Ó is replaced by Bean Uí ("wife of the grandson of") and Mac by Bean Mhic ("wife of the son of"). In both cases bean may be omitted, in which case the woman uses simply Uí or Mhic. Again, the second part of the surname is lenited (unless it begins with C or "G", in which case it is only lenited after Uí). Thus a woman marrying a man named Ó Dónaill may choose to be use Bean Uí Dhónaill or Uí Dhónaill as her surname; a woman marrying a man named Mac Gearailt may choose to use Bean Mhic Gearailt or Mhic Gearailt.

If the second part of the surname begins with a vowel, the form Ó attaches an h to it, as in Ó hUiginn (O'Higgins) or Ó hAodha (Hughes). The other forms effect no change: Ní Uiginn, (Bean) Uí Uiginn; Mac Aodha, Nic Aodha, Mhic Aodha, and so forth.

Mag is often used instead of Mac before a vowel or (sometimes) the silent fh. The single female form of "Mag" is "Nig". Ua is an alternative form of Ó.

Some names of Norman origin have the prefix Fitz, from Latin filius "son", such as Fitzwilliam, Fitzgerald, and so forth.