It seems this is a "faux de guerre" a war-scythe, popular in France from the 13th -15th century. A footman's arm, it was essentially a conventional scythe converted into a weapon. The problem with this is that the illustrations show something much more "refined" - it doesn't look patched together. Furthermore, it is wielded by men wearing maille, indicating some degree of wealth.
I'm thinking it is just another unconventional medieval weapon that was never standardized in any way. The various choppers in the
Maciejowski manuscript come to mind. It's just interesting to see these depicted.
Here's a pic of one I found: