Wikipedia
A twybil is a hand tool used for green woodworking. It is used for chopping out mortises when timber framing, or making smaller pieces such as gates. It combines chopping and levering functions in a single tool.
The appearance of a twybil is that of a T-shaped double-edged axe with unusually long blades and a very short handle. This appearance is deceptive, as they are actually derived from a large double-ended chisel with a side handle added for better control. The geometry of a twybil, particularly the long straight blades, makes it unworkable as an axe. Unfortunately many old examples have been damaged by such misuse. The related mortising axe or '' 'Bec d'ane' '' (donkey's nose) is similar, but single-sided and is forged and tempered to survive the shock loads of swinging as an axe.
Twybils always have two working ends and these are always different. The first is an axe-like blade, with the edge arranged parallel to the handle. The second edge is crossways, as for an adze. This is used for prying and levering rather than cutting.