Where does “Erse” come from?

Erse (English) comes from Scots Erse, from Middle English Irish, from Old English Īras, from Old Norse Írar, from Old Irish Ériu, from Primitive Irish *Īweriū, from Proto-Celtic Φīweryū, from Proto-Indo-European piHweryon- — fat, milk.

Erse (English): Either of the Gaelic languages of Ireland and...