It seems as though the word is related to the German for devil, Teufel, with the -ling suffix to denote offspring. I wonder if this is a genuine Old English word, or an artificial Teutonism. Dictionary.com doesn't list it as a word, and anything search engines list on this keyword is to do with RPG's and RPG fandom.
The German word Teufel interests me on its own. Does it derive from diabolos? The English devil, too, seems to have arrived from Greek the Saxon way, rather than Normandic.