Where does “onager” come from?

onager (Polish) comes from Ancient Greek ὄναγρος, from Ancient Greek Ἄγριος, from Proto-Indo-European h₂éǵr̥yos, from Proto-Indo-European h₂éǵros — field, pasturage.

Ancestry of “onager”, step by step

Step	Language	Word	Meaning
1	Ancient Greek	ὄναγρος	onager, wild ass; kind of catapult
2	Ancient Greek	Ἄγριος	living in the open fields
3	Proto-Indo-European	h₂éǵr̥yos	campestral, field attributive, of or relating to fields
4	Proto-Indo-European	h₂éǵros	field, pasturage

Every word from Proto-Indo-European h₂éǵros →Every word from Proto-Indo-European h₂éǵr̥yos →Every word from Ancient Greek Ἄγριος →