Alternative Form of Surnames

Rev Patrick Woulfe

Most of the patronymic surnames given above (§§ 1-2) have a second form obtained by dropping Ó or Mac and postfixing -ach (-each) to the nominative case of the name of the ancestor,* as Ó Briain or Brianach, Ó Broin or Branach, Ó Nualláin or Nuallánach, Mac Suibhne or Suibhneach.

This form is also used in the case of surnames of foreign origin, as Céitinn or Céitinneach (Céitneach), Dairsigh or Dairsigheach, Dalatún or Dalatúnach, Peitíd or Peitídeach. The prefix de is dropped when -ach is postfixed, as de Búrc or Búrcach, de Róiste or Róisteach. Surnames ending in -éil and éir change these terminations into -éal and -éar before -ach is added.

The foregoing forms when standing alone have an indefinite signification and cannot, unless defined by the context, be used to indicate a particular individual.† To make them definite they must be preceded by the Christian name or a title, or turned into one of the forms mentioned in the remaining paragraphs of this section, as: Domhnall Ó Briain, Cormac Mac Cárthaigh, Pádraig Condún, Éamonn de Búrc, Ualtar Caomhánach, An tEaspog Ó Domhnaill, An Dochtúir Ó Loingrigh.

The forms in -ach may also be made definite by prefixing the article and can then be used for a particular individual without the Christian name or title.‡ The form has then the force of the English Mr. when the Christian name is not expressed, as an Barrach, Mr. Barry; an Búrcach, Mr. Burke; An Brianach, Mr. O'Brien; an Suibhneach, Mr. MacSweeny.

Another way of indicating a particular individual, without using the Christian name, is to prefix Mac to the genitive case of the surname, as Mac Uí Bhriain, Mr. O'Brien, Mac Uí Chaoimh, Mr. O'Keeffe, Mac Mhic an Bháird, Mr. Ward. In this construction surnames commencing with Mac are sometimes treated as if they commenced with Ó, as: Mac Uí Ghearailt, Mr. Fitzgerald, Mac Uí Suibhne, Mr. MacSweeny.

We have also corresponding forms of -ach-surnames with the article, as: Mac an Bhreathnaigh, Mr Walsh, Mac an Bhúrcaigh, Mr. Burke; Mac an Róistigh, Mr. Roche.

* When the name of the ancestor already ends in -ach (-each) the termination is not repeated, as Ó Ceallaigh; or Ceallach, Ó Cinnsealagh or Cinnsealach.

† In the case of surnames in Ó and Mac, the name alone was formerly used as the title of the chief of the name, as Ó Néill, (The) O'Neill, Ó Domhnaill, (The) O Donnell; and it is still used as an honorary title in some families, as Ó Conchobhair Donn, The O'Conor Don, Mac Diarmada, The MacDermott.

‡ This -ach form with the article was formerly used, in the case of surnames of foreign origin, to signify the chief of an Anglo-Irish family, and corresponded to the use of the surname alone in the case of native Irish chiefs.