Yours, Etc.: Origins and Uses of 8 Sign-Offs
Old English Scottas (plural) "inhabitants of Ireland, Irishmen," from Late Latin Scotti (c.400), of uncertain origin, perhaps from Celtic (but answering to no known tribal name; Irish Scots appears to be a Latin borrowing). The name followed the Irish tribe which invaded Scotland 6c. C.E. after the Romans withdrew from Britain, and after the time of Alfred the Great the Old English word described only the Irish who had settled in the northwest of Britain.