The Sindarin cognate of Q. Melkor “He who arises in Might”, but this name was never used, being replaced with an altered form Belegurth “Great Death” (SI/Melkor, PM/358). The initial element of his name is beleg “mighty” and its final element is derived from primitive ✶ōre “arising”, hence literally: “Mighty Arising” (PE17/115). This Sindarin name indicates that the primitive form of his name must have begun with mb-: ✶Mbelekōre (PE17/115, WJ/402).
Conceptual Development: In the earliest Lost Tales, his Qenya name was ᴱQ. Melko and in the Gnomish Lexicon from the 1910s, its cognate was given as G. Belca >> Belcha from a root ᴱ√(M)BELEKE along with derivatives related to fire (GL/18, 22). In the Lays of Beleriand from the 1920s, the name was changed to ᴱN. Belegor >> Melegor (LB/21), but in Early Noldorin word lists from the 1920s the name appeared as ᴱN. Maileg (PE13/149).
In The Etymologies from the 1930s, the name changed to N. Maeleg >> Moeleg, derived from the root ᴹ√MIL(IK) along with derivatives related to greed and lust (Ety/MIL-IK). The form N. Moeleg appeared in Silmarillion drafts from the 1930s (SM/79, 164, 167). In later writings his Sindarin name was usually given as Belegûr, though in one place an alternate form Belchur was also given (PE17/115).
theon. Q. Melkor, Melkóre. >> Belchur