We are all aware of where the O’Neill name origins stem from; as it has been discussed accordingly during many debates in the forums and in the history section of our site.


However, another question that frequently arises concerns the difference between the ‘O’ and the ‘Mc’ (Mac) in people’s last names or (surnames). It is often sited that Scots use the ‘Mc’ and the Irish ‘O,’ but this is not necessarily the case,( there is a small basis of truth in this concept), however the Scots have their name origins tied directly to the Irish, based on our collective origins as members of the Celtic race or Diaspora. 


The Irish were among the first people in Europe to use surnames as we know them today. It is very common for people of Gaelic origin to have the English versions of their surnames beginning with "O'" or "Mc" (less frequently "Mac" and occasionally shortened to just "Ma" at the beginning of the name)."O'" comes from the Gaelic Ó which in turn came from Ua, which means "grandson", or "descendant" of a named person. Names that begin with "O'" include Ó Briain (O’Brien), Ó Cheallaigh (O’Kelly), Ó Conchobhair (O'Connor), Ó Domhnaill (O’Donnell), Ó Cuilinn (Cullen), Ó Máille (O’Malley), Ó Néill (O’Neill), Ó Sé (O'Shea), Ó Súilleabháin (O’Sullivan), and Ó Tuathail (O’Toole).


"Mac" or "Mc" means "son". Names that begin with Mac or Mc include Mac Diarmada (MacDermott), Mac Cárthaigh (MacCarthy), Mac Domhnaill (MacDonnell), and Mac Mathghamhna (MacMahon, MacMahony, etc.).




The proper surname for a woman in Irish uses the feminine prefix nic (meaning daughter) in place of mac. Thus a boy may be called Mac Domhnaill whereas his sister would be called Nic Dhomhnaill or Ní Dhomhnaill - the insertion of 'h' follows the female prefix in the case of most consonants (bar H, L, N, R, & T).


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.










The Mac Lochlainn, Ó Maol Seachlainn, Ó Maol Seachnaill, Ó Conchobhair Mac Loughlin and Mac Diarmada Mac Loughlin families, all distinct, are now all subsumed together as MacLoughlin. The full surname usually indicated which family was in question, something that has being diminished with the loss of prefixes such as Ó and Mac. Different branches of a family with the same surname sometimes used distinguishing epithets, which sometimes became surnames in their own right.




Later of course when the Irish and Scots began to travel overseas the question of last names or surnames took on a whole new direction with issue after issue. Last names began to lose their prefixes such as O and Mc however these individuals’ ancestors may have already lost them long before leaving either country.


This could have been based on the penal laws in Ireland and the British parliament bills of 1749 in Scotland both of which contained provisions in the destruction of clan culture, identity and its way of life including at times prefixes in names. The next issue concerning individual’s names was based on illiteracy of those Irish and Scottish traveling over seas however this was based on a foreign language English and Gaelic Languages were a non consideration.


The miss- understanding of those taking notes of individuals names concerning accents etc was also an issue at seaports etc therefore we see a constant variation of the spelling of names such as O’Neill, O’Neil, O’Neal, O’Neall, Neal etc however it should also be noted the correct spelling of the O’Neill name is the following (Ó Néill in Irish Gaelic) and (O’Neill in English).


O’Neill is one of the few names when spelt in both languages they are the same with the exception of a (fada accent piece) in the Irish spelling.