Wikipedia
Theodiscus
(the Latinised form of a Germanic word meaning "vernacular", "of the common people", or "native") is a Medieval Latin adjective referring to the Germanic vernaculars of the Early Middle Ages. It is the precursor to a number of terms in West Germanic languages, namely the English exonym Dutch, the German endonym Deutsch, and the Dutch exonym Duits and endonym Diets.
The word theodism, a neologism for a branch of Germanic neopaganism, is based on the Old English form of the word.