Origin of the word Mac

1. casual, generic term of address for a man, 1928, from Ir. & Gaelic mac, from O.Celt. *makko-s "son;" a common prefix in Scottish and Irish names, hence, used generally from early 19c. for a Celtic Irishman. Cognate root *makwos "son" produced O.Welsh map, Welsh mab, ap "son;" also probably cognate with O.E. mago "son, attendant, servant," O.N. m?gr "son," Goth. magus "boy, servant," O.E. m?g? "maid" (see maiden).

via Online Etymology Dictionary, ©2001 Douglas Harper