Named after Donnybrook Fair, infamous in the 19th century for its faction fights; long since gentrified. 'It has turned into a veritable donnybrook', Apu watching mob warfare unfold in one episode of The Simpsons
The endemic misuse of this word as a synonym for 'perimeter' - i.e. "within those parameters" - is a constant source of irritation for me. The French have both 'périmètre' and 'paramètre' and manage not to confound them.