Mac Prefix
Mac / Mc
A Gaelic patronymic prefix meaning 'son of', used in Irish and Scottish surnames to indicate descent from a named male ancestor.
The prefix Mac (sometimes written Mc, an abbreviation of the same element) derives from the Old Irish word mac, meaning 'son'. It forms the first element of patronymic surnames across both Ireland and Scotland, indicating that the original bearer was the son of the person named in the second element. MacCarthy, for example, means 'son of Carthach', and MacDonald means 'son of Domhnall'. The prefix is one of the most immediately recognizable markers of Gaelic heritage in the Anglophone world.
Historical Development
In early medieval Ireland, Mac functioned as a literal descriptor within a fluid patronymic system: a man named Conchobar Mac Briain was simply identified as 'Conchobar, son of Brian'. Hereditary surnames — where Mac became fixed across generations — began solidifying in Ireland from roughly the tenth century onward, making Irish surnames among the earliest hereditary family names in Europe. The anglicization of Mac surnames during colonial administration introduced spelling variations including Mc, M', and occasionally plain Mac without a capital on the following letter. All three forms are orthographically equivalent.
Modern Usage
Today Mac and Mc surnames are borne by millions of people of Irish and Scottish descent worldwide. Irish law treats Mac and Mc as the same prefix, and Irish-language forms retain the full Mac spelling (e.g., Mac Cárthaigh). In Irish grammar, the prefix undergoes lenition for daughters and wives: a son is Mac Cárthaigh, but his sister is Nic Cárthaigh — the Nic form being a contraction of Nighean Mhic, meaning 'daughter of the son of'.