1 a non-Traveller man married to a Traveller: Never in my born days have I heard of such a thing among Travellers. They will marry blue-bucks, you see. 20-.
2 a filthy vagrant 20-: Compare buck and buck union etymology: blue ‘perhaps relating to the colour’ + buck ‘a male animal’; sense 2 collected by EMcC/PS; attested by JS and BW