Where does “Erse” come from?

Erse (Scots) comes 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-, from Proto-Indo-European peyH- — fat, milk.

Erse (Scots): Irish