hair (verb) — sense 4

Now know ye, that in compliance with the said proviso, we the said John Cant and John Millar do hereby declare that our said invention of a new method of tanning leather is described in the manner following : that our method of preparing hides and skins by liming, hairing, fleshing, and baiting, is the same as that in use by the most experienced tanners; that is to say: All leather that is to be dressed or curried, we use the operation of what tanners call baiting, for this reason; that the leather when curried should carry a sufficient quantity of oil, and dry a good colour.