It's a 'gunstock club', a weapon which possibly derives its shape from european muskets, which were sometimes used as two-handed clubs when they weren't able to be loaded in time. Or possibly it just vaguely resembled a musket by sheer coincidence.

As /u/looksatanimals said, it's a gunstock club. Let me address a common misconception about them. Some say that they were made from the stocks of damaged longrifles or from stocks which had been messed up during the process of carving from a blank. This is myth. A longrifle stock is too slender and made from too brittle wood to be used to make an axe or a war club. These were built from the ground up for their purpose.