A root in The Etymologies of the 1930s with derivatives having to do with quickness, suddenness and fierceness (Ety/BERÉK), replacing rejected ᴹ√MEREK and ᴹ√BHERÉK (Ety/MERÉK; EtyAC/MERÉK). One notable derivative is the name N. Bregolas “Fierceness”, which continued to appear as S. Bregolas (albeit untranslated) in later versions of The Silmarillion (S/148). It seems likely this root was also an element in the name Bregalad “Quickbeam”, first introduced in Lord of the Rings drafts from the 1940s (TI/419) and retaining this form and meaning thereafter (LotR/482).
One of the 1930s derivatives of this root was N. Dagor Vregedúr “Battle of Sudden Fire [bregedur]”, which in the published Silmarillion became S. Dagor Bragollach “Battle of Sudden Flame” (S/151). This hints at a possible revision of this root, perhaps to ✱√BARAK, though whether it was a transient or lasting change is unclear.
Neo-Eldarin: For purposes of Neo-Eldarin writing, I think it’s best to stick with ᴹ√BEREK and the forms from The Etymologies.