or Byrlaw. A sort of Lynchlaw in the rural districts of Scotland. The inhabitants of a district used to make certain laws for their own observance, and appoint one of their neighbours, called the Burlaw-man, to carry out the pains and penalties. The word is a corrupt form of byr-law, byr=a burgh, common in such names as Derby, the burgh on the Derwent; Grimsby (q.v.), Grims-town.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894