Where does “αντιδραστικός” come from?

αντιδραστικός (Greek) comes from Greek αντί-, from Ancient Greek ἀντι-, from Ancient Greek ᾰ̓ντῐ́ — opposite.

αντιδραστικός (Greek): reactive; reactionary

Definitions

Step	Language	Word	Meaning
1	Greek	αντί-	Alternative form of αντι-; counter; opposite to
2	Ancient Greek	ἀντι-	anti-, against; like, reminiscent of
3	Ancient Greek	ᾰ̓ντῐ́	opposite

αντιδραστικός — Etymology, Origin & Word History | Etymology Explorer