The form bronio in the Etymologies is a misreading according to VT/45:7
Noldorin
dartha-
verb. to wait, stay, remain, last, endure
dartha-
verb. to wait, stay, last, endure, remain
dar-
verb. to stay, wait, stop, remain
brenia-
verb. to endure
brona-
verb. to last, to survive
A verb in The Etymologies of the 1930s glossed “wait, stay, last, endure” under the root ᴹ√DAR “stay, wait, stop, remain” (Ety/DAR).