Where does “ἱερο-” come from?

ἱερο- (Ancient Greek) comes from Ancient Greek ἱερός, from Proto-Hellenic iherós, from Proto-Indo-European ish₁ros.

Ancestry of “ἱερο-”, step by step

Step	Language	Word	Meaning
1	Ancient Greek	ἱερός	connected with the gods, supernatural; holy,...
2	Proto-Hellenic	iherós	—
3	Proto-Indo-European	ish₁ros	—

ἱερο- — Etymology, Origin & Word History | Etymology Explorer