"Mac" is the word for "son" both in Irish and Scottish. Here’s some more detailed info (taken from
here, not from my memory

):
"The prefix Mac (also spelled Mc or less commonly M' or M with a superscript c) is extremely common in family names of Irish or Scottish Gaelic origin. Mac is the Irish and Scottish Gaelic word for "son," and is thus equivalent to the element -son in family names of English origin. It also appears, especially in Scottish names, before the names of saints or before occupational names (e.g. McWhirter, from a Scottish Gaelic word for 'harpist'). Mac always appears before a name, like Fitz- in "Fitzgerald," which is from Anglo-French fi(t)z 'son'. In Gaelic Mac is usually written as a separate word; Macdonald, for example, is an Anglicized version of Mac Dhomhnuill.
Mac is related to words for "son" in other Celtic languages also, notably Welsh and Cornish mab, which in Old Welsh was map (the relationship between the "k" sound in Irish and Scottish Gaelic and the "p/b" sound in Welsh is a regular feature of these languages). Map gave rise to the Welsh prefix Ap, which is equivalent to Mac but is less common; one example is the family name Price, a reduction of Ap Rhys 'son of Rhys'.
The use of hereditary surnames arose in Ireland much earlier than in most countries. These names, with Mac or Ó (which means 'grandson or descendant of'), were often shared by the members of a clan or a group living in the same region even if they did not have a common ancestor."
Welcome to the forum, btw!
