billhook
A billhook is a tool for cutting branches and grape vines, usually with a curved, concave sickle-like blade. The length of the blade and handle varies.
The weapon version of the billhook is a polearm typically with a pointed spearhead and back spike or hook in addition to the curved blade, similar to a halberd.
Don't mix this up with the similar hashitsuki nata and nata (tool), which usually have a flat side and for which the "nose" is perpendicular to the blade, while the end of billhooks curves downward.