Where does “do-” come from?

do- (Manx) comes from Old Irish do-, from Proto-Celtic dus-, from Proto-Indo-European dus-, from Proto-Indo-European dēwǝ- — to fail, be behind, be lacking.

do- (Manx): non-, un-

Definitions

non-, un-

Ancestry of “do-”, step by step

Step	Language	Word	Meaning
1	Old Irish	do-	impossible, extremely difficult; ill, evil;...
2	Proto-Celtic	dus-	bad
3	Proto-Indo-European	dus-	bad
4	Proto-Indo-European	dēwǝ-	to fail, be behind, be lacking

Words derived from “do-”

do-iu
do-varganagh
do-smooinaghtyn

Every word from Proto-Indo-European dēwǝ- →Every word from Proto-Indo-European dus- →Every word from Old Irish do- →