Mac means 'the son of' an dis sometimes anglicized as "Mc" which loses all meaning. Several thousand Irish dropped the 'o' and 'mac' from their names when they went to America so their names would appear less Irish. the old families are believed to have a banshee attached to them. An old poem went as follows:
Per O' atque Mac, veros cognoscis Hibernos;
His duobus demptis, nullus Hibernus adest.
Which has been translates as
"By Mac and O' you'll always know
True Irishmen, they say:
But, if they lack the O' or Mac,
No Irishmen are they