Where does “Hh₃os-k-yeh₂-” come from?

Hh₃os-k-yeh₂- (Proto-Indo-European) comes from Proto-Indo-European Heh₃s- — ash tree.

Ancestry of “Hh₃os-k-yeh₂-”, step by step

Step	Language	Word	Meaning
1	Proto-Indo-European	Heh₃s-	ash tree