Mac
or Mc, a Gaelic prefix signifying son. Macaulay is equivalent to son-of-Aulay, or Aulayson, as the name would appear in a Teutonic language. The prefix is borne chiefly by natives of Scotland and Ireland and their descendants. In Scotland it indicates Highland ancestry. In Ireland a popular rhyme runs:
By Mac and O you always know
True Irishmen, they say:
For if they lack both O and Mac,
No Irishmen are they.
True Irishmen, they say:
For if they lack both O and Mac,
No Irishmen are they.
Volume III · Aiton’s Encyclopedia