Where does “napolje” come from?

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

napolje (Serbo-Croatian): outside

Definitions

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

napolje — Etymology, Origin & Word History | Etymology Explorer