Where does “Ίσις” come from?

Ίσις (Greek) comes from Ancient Greek Ἶσις, from Egyptian ꜣst — Isis.

Ancestry of “Ίσις”, step by step

Step	Language	Word	Meaning
1	Ancient Greek	Ἶσις	Isis
2	Egyptian	ꜣst	Isis

Ίσις — Etymology, Origin & Word History | Etymology Explorer