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for noun 1: of unknown origin: The Promp. Parv. explains ‘Breyel’ as brollus, brolla, miserculus; but this may be merely the English word latinized. It seems possible that, as brethel was app. reduced to breel, brothel may have been reduced to brōl, but evidence is wanting.
for verb: ? by-form of brawl v., or ? from Dutch brullen to roar
From: A New English Dictionary on Historical Principles, James Murray, 1888-1933