Among the Gaelic-speaking Irish, traditional family names form a couple of interesting and complex paradigms. Whereas most European languages have a way of addressing the marital status of women, but not men, with a separate word (eg. English "Miss" versus "Mrs."), in Irish, it is the family name itself that changes to reflect this fact. (Again, only in the case of women.)
The two paradigms are based on whether the family name begins with "Mac" or "O". (For simplicity's sake, I have elected to not use any accents in these examples, though vowels in Irish are sometimes written with an acute accent over them.) "Mac" meaning "son of", and "O" literally meaning "from, of" and in this context, "descended from".
The unmarried daughter of a man whose surname begins with "Mac" would instead have the prefix "Nic", followed by a slightly-modified form of the surname itself. The wife of a man whose surname begins with "Mac" would instead have the prefix "Mhic", followed by the same slightly-modified surname as the daughter.
As an example:
Sean Mac Brogan, whose wife would be
Maire Mhic Bhrogan, and whose unmarried daughter would be
Sinead Nic Bhrogan.
The case is much the same in the paradigm of "O" names. For the wives of men with such names, the prefix would instead be "Ui", and for the unmarried daughters, it would be "Ni".
Another example:
Colm O Braonain, whose wife would be
Aine Ui Bhraonain, and whose unmarried daughter would be
Nuala Ni Bhraonain.
Seeing as how the use of Gaelic has greatly declined within Ireland, these name practices are more or less disappearing. The interesting thing to note is that when traditional Gaelic family names become anglicized, one of two things will happen: the prefixes disappear altogether, or everybody uses the male form of the family name.
(Rough) Pronunciation Guide:
Mac - more like "mock" than "mack"
Nic - "nick"
Mhic - "vick"
O - "oh"
Ui - "ee"
Ni - "nee" | 
