Where does “ναι” come from?

ναι (Greek) comes from Ancient Greek ναί, from Ancient Greek νή, from Proto-Indo-European h₁énos, from Proto-Indo-European h₁é, from Proto-Indo-European ǵʰe — Postpositional intensifying particle: indeed, at any rate, in fact.

ναι (Greek): yes

Definitions

Ancestry of “ναι”, step by step

Step	Language	Word	Meaning
1	Ancient Greek	ναί	yea, verily; yes
2	Ancient Greek	νή	by; 430 BCE – 354 BCE, Xenophon, Cyropaedia
3	Proto-Indo-European	h₁énos	that, that over there, yon
4	Proto-Indo-European	h₁é	and, then
5	Proto-Indo-European	ǵʰe	Postpositional intensifying particle: indeed, at any rate, in fact

Every word from Proto-Indo-European ǵʰe →Every word from Proto-Indo-European h₁é →Every word from Proto-Indo-European h₁énos →