Where does “odpovědět” come from?

odpovědět (Czech) comes from Czech od-, from Old Czech ot-, from Proto-Slavic otъ-.

Ancestry of “odpovědět”, step by step

Step	Language	Word	Meaning
1	Czech	od-	A prefix, usually indicating movement away,...
2	Old Czech	ot-	—
3	Proto-Slavic	otъ-	—

odpovědět — Etymology, Origin & Word History | Etymology Explorer