Where does “натопити” come from?

натопити (Serbo-Croatian) comes from Serbo-Croatian на, from Proto-Slavic na, from Proto-Indo-European h₂en- — on, onto.

Ancestry of “натопити”, step by step

Step	Language	Word	Meaning
1	Serbo-Croatian	на	to, on, onto; on, at, in; by, for, at
2	Proto-Slavic	na	on; concerning; onto
3	Proto-Indo-European	h₂en-	on, onto

натопити — Etymology, Origin & Word History | Etymology Explorer