It’s not. We did a round on scythes last year, but the short version is that scythes aren’t weapons, and they don’t really adapt well for use as weapons.
Now, there is a pole-arm called a war scythe, which is similar in that there’s a stick and a blade, but, the blade projects out in line with the shaft, like a halberd or other bladed polearm, and the shaft itself is straight. So, if you really want a slightly curved blade on your spear or pike…
Anyway, scythes were designed for harvesting crops, the design requires that you pull towards you to cut. This is a very bad thing on so many levels in combat. First, you’re actually pulling your blade towards you, inviting you to disembowel yourself, second you can’t defend yourself from someone closing in. Yeah, just don’t have your characters try to fight with one.