This is indeed a coupe-marc / couteau à marc / couteau de pressoir, most likely from the XIXth century (XVIIIth being possible too). The shape is characteristic, and is one of the most widely used for this kind of tool.
Although some tools were indeed used as polearms, or evolved into them, this is way too heavy to be used effectively as a weapon.
Similar examples coming from museums in Normandie (a well known cider producing region of France):
https://collections.musees-normandie...b-8568daf8c665
https://collections.musees-normandie...b-8568daf8c665
https://collections.musees-normandie...b-8568daf8c665