(pl.) "inhabitants of Ireland, Irishmen," from L.L. Scotti
(c.400), of uncertain origin, perhaps from Celtic (but answering to no known tribal name; Ir. Scots
appears to be a L. borrowing). The name followed the Irish tribe which invaded Scotland after the Romans withdrew from Britain in 423 C.E., and after the time of Alfred the Great the O.E. word described Irish who had settled in the northwest of Britain.
"Scot, with its variants Scotch, Scottish, etc., may have been an Irish term of scorn (Scuit, pronounced shite); its ulterior origin is unknown." [Shipley]