Where does “Αἰθήρ” come from?

Αἰθήρ (Ancient Greek) comes from Ancient Greek αἴθω, from Proto-Hellenic *áitʰō.

Αἰθήρ (Ancient Greek): Upper Air

Definitions

Step	Language	Word	Meaning
1	Ancient Greek	αἴθω	To ignite, kindle, light; To burn, blaze
2	Proto-Hellenic	*áitʰō	—

Αἰθήρ — Etymology, Origin & Word History | Etymology Explorer