Interesting thread...
Here is a regional billhook from the area where i live.
It is called "Haubergsknipp" or just "Knipp".
It is used in a traditional kind of woodland management called "Hauberg" for clearing out the underbrush and removing small twigs. The bill was used to scarify the bark of the trees so it could be peeled. The bark was harvested as tanning agent. The wood was used to make charcoal.
http://www.hauberg.onlinehome.de/de/jahreslauf.html
Sadly, i couldn't find any english language description decription
The depicted specimen is roughly 100 years old and has been used for at least 70 years.
Best Regards
Thilo