Incidentally, in the Slaine comics based on Celtic myth 'orc' is used as an alternative word for the Fomorians, monstrous humanoids from the northern seas (drawn a bit like D&D sahuagin), ie this fits with the 'Orkney' islands as a source. I think the old-English ogre-orcs may have been related to the Greek sea-orcs. Our modern RPG "horde of minor goblinoid" orcs are definitely 100% Tolkien, though.