Where does “چی” come from?

چی (Persian) comes from Middle Persian 𐭬𐭤 — what, which; for, because.

چی (Persian): API •; what?; -er; -eer

Definitions

Step	Language	Word	Meaning
1	Middle Persian	𐭬𐭤	what, which; for, because

چی — Etymology, Origin & Word History | Etymology Explorer