burl |bərl|nouna slub or lump in wool or cloth.• a rounded knotty growth on a tree, giving an attractive figure when polished and used esp. for handcrafted objects and veneers : she used warty burls to construct her pieces | wooden coin banks made of elm burl| [as adj. ] a burl bowl.ORIGIN late Middle English : from Old French bourle‘tuft of wool,’ diminutive of bourre ‘coarse wool,’from late Latin burra ‘wool.’
I learned this word thanks to television. Apparently, there are people called "burl hunters," who make a living finding and harvesting these things.