Where does “*इष्टा” come from?

*इष्टा (Sanskrit) comes from Sanskrit इष्टका, from Proto-Indo-Iranian Hišt- — brick.

Ancestry of “*इष्टा”, step by step

Step	Language	Word	Meaning
1	Sanskrit	इष्टका	brick; bakestone
2	Proto-Indo-Iranian	Hišt-	brick

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