A hard protuberance with twisted grain on a tree.

ETYM Prov. Eng., n, a lump on a tree where a branch has been cut off.
1. Any hook-like protuberance.
2. A stump or base of a branch that has been lopped off; a short branch, or a sharp or rough branch.
3. A small problem.
4. A catch in a fishing line when the hook has caught on weeds or other matter below the surface.