The Adûnaic name of Morgoth; it seems to be a loan word from Q. Melkor “Mighty Arising” (or some Avari variant of it), but it is glossed “Lord of Darkness” (SD/358). If this is the meaning of the word, the final element could be related to khôr “lord” appearing in the later name Adûnakhôr “Lord of the West”, or to the older rejected name Kherû “Lord”, also referring to Melkor. The initial element Mul- could perhaps a distant variation on the Elvish root √MOR “dark”. Yet another possibility is that it was originally an ancient Elvish loan word (✶milikûr?) that shifted in form to resemble the meaning “Lord of Darkness”.
Conceptual Development: The first Adûnaic for Morgoth, Mēlekō, was more clearly based on ᴹQ. Melko, which was the Quenya name for Melkor in that stage of Tolkien’s writing.