Where does “Hindu” come from?

Hindu (Hungarian) comes from Proto-Indo-Iranian síndʰuš, from Sanskrit सिन्धु॑.

Ancestry of “Hindu”, step by step

Step	Language	Word	Meaning
1	Proto-Indo-Iranian	síndʰuš	river, stream
2	Sanskrit	सिन्धु॑	—

Hindu — Etymology, Origin & Word History | Etymology Explorer