MORGUE.  An early French form of Morgan (q.v.), from Morgáin (q.v.), used by Chrétien, meaning "great queen." 

... From the fact that in such early material Morgan is a nominative it seems rather more likely that an analogical nominative, Morgue, was formed from Morgan (ain), than that the reverse process took place, namely that Morgain is an analogical accusative, which in the Roman de Troie is already obtruding upon the nominative, as it certainly did in the thirteenth century... (Studies in the Fairy Mythology of Arthurian Romance, Paton, 1903).