Where does “dyć” come from?

dyć (Polish) comes from Welsh dy-, from Proto-Celtic dus-, from Proto-Indo-European dus-, from Proto-Indo-European dēwǝ- — to fail, be behind, be lacking.

Ancestry of “dyć”, step by step

Step	Language	Word	Meaning
1	Welsh	dy-	bad; to, together
2	Proto-Celtic	dus-	bad
3	Proto-Indo-European	dus-	bad
4	Proto-Indo-European	dēwǝ-	to fail, be behind, be lacking

Every word from Proto-Indo-European dēwǝ- →Every word from Proto-Indo-European dus- →Every word from Welsh dy- →