Where does “ostawić” come from?

ostawić (Polish) comes from Old Polish ostawić, from Old Polish o-, from Proto-Slavic o(b)- — over.

Ancestry of “ostawić”, step by step

Step	Language	Word	Meaning
1	Old Polish	ostawić	to leave
2	Old Polish	o-	appears in front of some verbs meaning: to make something behave in a certain way, en-, be-, make
3	Proto-Slavic	o(b)-	over