Ponmecainne, Pomytayn
Duke Galeholt gave this island as a gift to King Marsil of Pomitain.
Assuming it was one of the Long Isles, and that the Long Isles were Islay, Jura, Kintyre, and Arran, P.A. Karr would make Arran Pomitain. It might, of course, have been another of Galeholt’s conquests entirely.
Sources
Prose Tristan | 1230-1240
Le Morte Darthur | Sir Thomas Malory, 1469-1470