Where does “dolnyā” come from?

dolnyā (Proto-Celtic) comes from Proto-Indo-European dʰelh₁- — blossom; be green; to bloom, be green.

Ancestry of “dolnyā”, step by step

Step	Language	Word	Meaning
1	Proto-Indo-European	dʰelh₁-	blossom; be green; to bloom, be green

dolnyā — Etymology, Origin & Word History | Etymology Explorer