The great fire demons of Melkor, a combination of the root √BAL “power” with raug “demon” (SA/rauko, val; PE17/48).
Conceptual Development: The name G. Balrog appeared in the earliest Lost Tales (LT1/93) and always kept this form in Tolkien’s writings, but its meaning and etymology evolved over time: G. “a kind of fire demon” (GL/21), ᴱN. “evil demon” (PE13/138), N. “✱Torment Demon” (Ety/ÑGWAL, RUK), an untranslated orc word (LR/404) and finally S. “Mighty Demon” (PE17/48).
Quenya name for a Balrog, a combination of some derivative of the root √BAL “power” with rauco “demon” (SA/rauko, val; PE17/48). It also appeared as Valarauka (PE17/48).
Conceptual Development: In the Qenya Lexicon from the 1910s, their name was either ᴱQ. Valkarauke “✱Cruel Demon” or ᴱQ. Malkarauke “✱Torment Demon” (QL/58, 60, 101-2). In The Etymologies from the 1930s, the second form reappeared as ᴹQ. Malarauko of similar meaning (Ety/RUK), but in this conceptual period it seems to be a loan word from either Noldorin or Orcish (LR/404). The forms Valarauka or Valarauko emerged in Tolkien’s later writing (PE17/48, WJ/415).