Where does “नहीं” come from?

नहीं (Braj) comes from Sanskrit नहि, from Proto-Indo-Iranian naǰʰí, from Proto-Indo-European ǵʰe.

नहीं (Braj): not

Definitions

Step	Language	Word	Meaning
1	Sanskrit	नहि	surely not, by no means, not at all
2	Proto-Indo-Iranian	naǰʰí	—
3	Proto-Indo-European	ǵʰe	—

नहीं — Etymology, Origin & Word History | Etymology Explorer