taken from a welsh dic; du = black, god = duw,and goddess = duwies. God also has du in its makeup, giving rise to a black god as in irish mythology. Taking the other part of the word,(in welsh this is) ergyd= a blow, and ergydio= to strike. Not exactly a match but interesting, this other half could have a meaning to strike as in dwarf (old blacksmiths?) Goblins/gods. Of course it could all be nonsense.....