The form brerg in the Etymologies is a misreading according to VT/45:34
Noldorin
lothren
adjective. wild, waste
Eru
noun. waste, desert
braig
adjective. wild, fierce
breig
adjective. wild, fierce
rhaw
adjective. wild, untamed
Meaning rectified according to VT/46:10
The form brerg in the Etymologies is a misreading according to VT/45:34