A war scythe or military scythe is a form of polearm with a curving single-edged blade with the cutting edge on the concave side of the blade. Its blade bears a superficial resemblance to that of an agricultural scythe from which it is likely to have evolved, but the war scythe is otherwise unrelated to agricultural tools and is a purpose-built infantry melee weapon. The blade of a war scythe has regularly proportioned flats, a thickness comparable to that of a spear or sword blade, and slightly curves along its edge as it tapers to its point. This is different from farming scythes, which have very thin and irregularly curved blades, specialised for mowing grass and wheat only, unsuitable as blades for improvised spears or polearms.

A polearm or pole weapon is a close combat weapon in which the main fighting part of the weapon is fitted to the end of a long shaft, typically of wood, extending the user's effective range and striking power. Polearms are predominantly melee weapons, with a subclass of spear-like designs fit for thrusting and/or throwing. Because many polearms were adapted from agricultural implements or other fairly abundant tools, and contained relatively little metal, they were cheap to make and readily available. When belligerents in warfare had a poorer class who could not pay for dedicated military weapons, they would often appropriate tools as cheap weapons. The cost of training was comparatively low, since these conscripted farmers had spent most of their lives using these "weapons" in the fields. This made polearms the favoured weapon of peasant levies and peasant rebellions the world over.