Where does “отчаяться” come from?

отчаяться (Russian) comes from Russian от-, from Proto-Slavic otъ-.

Ancestry of “отчаяться”, step by step

Step	Language	Word	Meaning
1	Russian	от-	away from
2	Proto-Slavic	otъ-	—

отчаяться — Etymology, Origin & Word History | Etymology Explorer