... The Gaelic or Celtic orc and the Spanish orc-o signify a whale; and Milton employs the word orc in the same sense—"The haunts of seals and orcs and sea-mews clang."  In Gaelic the Orkneys are called Orcinnse, Whale-isles, and, in the Ossianic poems, Innistorc, a name of the same import.  By the Northern Gael Orkney is, at this day, called Orc-adh or Arc-adh.  The primary signification, then, of the root orc seems to be bulkiness, implying strength.  It may be mentioned, in passing, that, in old Gaelci, the word A denotes a promontory.  As to the termination, -ey, in Norse or Icelandic, signifies an island,—the plural being -eys... (Ancient History of Orkney, Caithness, and the North, Torfaeus-Pope, 1866).

... I do not know of any work in which Gawain's mother is named Morcades earlier than the continuation of Chrétien's Perceval ascribed to Wauchier de Denain who flourished at the end of the 12th and beginning of the 13th century... as far as I can discover, the name occurs only in Heinrich von dem Türlin's Diu Crône as a variant of Orcades—in that poem the usual name of Gawain's mother... Miss L.A. Paton (Studies in the Fairy Mythology of Arthurian romance), says "Morchades (Marcades) is perhaps merely a mistake for Orcades, the name of the kingdom which she and Loth ruled over.  But the inventor of the name probably intentionally prefixed the M to make it alliterate with the name of her sister Morgain. (Historia Meriadoci and De ortu Waluuanii, Bruce, 1913)