Quenya 

mori-

dark, black

mori- "dark, black" in a number of compounds (independent form morë, q.v.):Morimando "Dark Mando" = Mandos (MBAD, VT45:33), morimaitë "black-handed" (LotR3:VI ch. 6, VT49:42). Moriquendi "Dark Elves" (SA:mor, WJ:361, 373), Moringotto "Black Foe", Sindarin Morgoth, later name of Melkor. The oldest form is said to have been Moriñgotho (MR:194). In late material, Tolkien is seen to consider both Moringotto and Moricotto _("k") _as the Quenya form of the name Morgoth (VT49:24-25; Moricotto also appears in the ablative, Moricottollo). Morion "the dark one", a title of Morgoth (FS). Morifinwë "dark Finwë", masc. name; he was called Caranthir in Sindarin (short Quenya name Moryo). (PM:353) In the name Morinehtar, translated "Darkness-slayer", the initial element is defined would thus seem to signify "darkness" rather than "dark" as an adjective (see mórë). (PM:384, 385)