Where does “derg” come from?

derg (Old Irish) comes from Proto-Celtic dergos, from Proto-Indo-European dʰerg-, from Proto-Indo-European dʰer- — to support; to hold.

derg (Old Irish): red

Definitions

Step	Language	Word	Meaning
1	Proto-Celtic	dergos	red crimson
2	Proto-Indo-European	dʰerg-	to dim, darken; dim, dull; dark, dusky
3	Proto-Indo-European	dʰer-	to support; to hold

derg — Etymology, Origin & Word History | Etymology Explorer