Where does “οξύ” come from?

οξύ (Greek) comes from Ancient Greek ὀξύς, from Proto-Indo-European h₂eḱ- — sharp.

οξύ (Greek): acid

Definitions

Step	Language	Word	Meaning
1	Ancient Greek	ὀξύς	sharp, pointed; sharp, keen; quick, hasty, swift
2	Proto-Indo-European	h₂eḱ-	sharp

οξύ — Etymology, Origin & Word History | Etymology Explorer