Where does “*चिष्ट” come from?

*चिष्ट (Sanskrit) comes from Proto-Indo-Aryan ćiṣṭás — message.

Ancestry of “*चिष्ट”, step by step

Step	Language	Word	Meaning
1	Proto-Indo-Aryan	ćiṣṭás	message

*चिष्ट — Etymology, Origin & Word History | Etymology Explorer