Antique 3 Sided Edged Tool/Weapon Mound Tool Co. Help I.D.

This is one of the few items found in old tool box last week. I have no idea what its used for or if its even a tool. It is stamped mound tool co. On the blade. This measures from handle to top 12inches. The blade is 8 in long. This is 3 sided and edged and still sharp I almost cut myself twice already on it. I was hoping someone could help me ID this piece. I dont know if this was once a bayonet blade or a tool designed for a purpose. Thanks