The Sindarin word for “great” which appears in names like Belegaer “Great Sea” (S/37), Belegurth “Great Death” (PM/358), and especially the name Beleg (SA/beleg). Like English, the word beleg can mean “great” = “mighty” as well as “great” = “large” (PE17/115), but unlike English does not mean “great” = “good”.
Possible Etymology: The Etymologies of the 1930s had N. beleg “great” derived from ON. beleka “mighty, huge, great” under the root ᴹ√BEL “strong” (Ety/BEL). In this document, the name ᴹQ. Melko was derived from unrelated ᴹ✶Mailikō under the root ᴹ√MIL-IK having to do with greed and lust (Ety/MIL-IK). Notes on The Feanorian Alphabet from the 1930s and 40s show the mutated form feleg [veleg] “large” or “great” (PE22/31; PE23/20, 51).
At some point Tolkien reconceived of the etymology of Melkor’s names as being derived from ✶mbelekōro “He who arises in Might” (WJ/402), and in notes on “large & small” roots from 1968 Tolkien also connected this primitive form to S. beleg (PE17/115). This would imply specialized mutations for beleg as derived from an ancient nasalized stop mb-. However, attested mutations imply the primitive form of beleg began with b-, such as Cûl Veleg “Big Load” (RC/536) or Taur-i-Melegyrn “Forest of the Great Trees” (WJ/185).
Neo-Sindarin: For purposes of Neo-Sindarin, I would assume the strengthening of the ancient initial consonant to mb- occurred only in Quenya to explain the Sindarin mutations demonstrating primitive initial b-.
Conceptual Development: This word dates all the way back to the earliest forms of the language, no doubt due to the influence of the name Beleg which was equally old. The Gnomish Lexicon of the 1910s had G. Beleg “mighty, great” (GL/22). ᴱN. beleg “great, large” appeared in the Early Noldorin Grammar of the 1920s (PE13/125), and beleg “huge” appeared in Early Noldorin word-lists from this same period (PE13/138). N. beleg “great” appeared in The Etymologies of the 1930s as noted above (Ety/BEL), and this word continued to appear regularly in Tolkien’s writings thereafter.
A hero of Doriath and friend of Túrin (S/200). His name is simply the adjective beleg “mighty” used as a name (SA/beleg).
Conceptual Development: The name G. Beleg dates back to the earliest Lost Tales, already having its later etymology (LTA2/Beleg). The name reappeared in the Lays of Beleriand from the 1920s (LB/30), and again in Silmarillion drafts from the 1930s (LR/287). In The Etymologies, Beleg was designated an Ilkorin name, translated “Strong” (Ety/BEL).