This is an early style of spontoon, often regarded as French, though they appear throughout Western Europe and early New World settlements.
The spontoon was not only a weapon but also a badge of rank. It was generally carried by an officer of infantry on land, or by sailors and marines at sea. They were clumsy to use on deck so they were usually confined to boarding parties or shore raids when used by mariners.
This is an early style of spontoon, often regarded as French, though they appear throughout Western Europe and early New World settlements. It has been well used and shows its age. Originally it was probably kept sharp and polished, it is now dulled and has a worn finish. The head is socket mounted on a blackened staff by rivets. Certainly a later shaft but appropriate for its early style.
I would date this weapon from the late 1600's to perhaps 1760. The blade and socket measure 17" (44cm). The blade and staff together are 81" (210cm) tall. I have had this in my collection for 20+ years.