Fourth great battle of the Wars of Beleriand, translated “Battle of Sudden Flame” (S/151), a combination of dagor “battle” and bragollach “sudden flame” (possibly = “wild fire”).
Conceptual Development: In Silmarillion drafts from the 1930s, this battle was first named N. Dagor Húr-Breged “Battle of Sudden Flame” (SM/317) or “Fire” (LR/132). This was revised to N. Dagor Vregedúr “Battle of Sudden Fire” (LR/280), a form that also appeared in The Etymologies where the second element was indicated to be the lenited form of N. bregedur “wild fire” (Ety/BERÉK). The name took on its final form in Silmarillion revisions from the 1950s-60s (WJ/52, 124).
An element in the name Dagor Bragollach “Battle of Sudden Flame” (S/151; WJ/52), a replacement for earlier N. Dagor Vregedúr “Battle of Sudden Fire”.
Neo-Sindarin: Elsewhere all the words for “sudden” began with breg-, such as in Bregalad “Quickbeam” (LotR/482), so despite its possible replacement, I prefer the earlier word N. bregedur “wild fire”. If bragollach is used, I’d revise it to ✱bregollach.