 Second element may be Celtic *"landā" 'land, place' (Welsh "llan"); or, *"plan-" > *"lan-", a Celtic cognate of Latin "plānus" 'plain', with typical Celtic loss of /p/.From Celtic *Bhel- 'bright' and *dūnon 'fortress'.From Celtic *"brigant-" 'high, lofty, elevated' (or divine name, Brigantia)
From Celtic *briga- 'rocky height or outcrop'.