An Etymological Dictionary of the German Language/Annotated/Teufel
Teufel, masculine, ‘devil, demon,’ from the equivalent Middle High German tiuvel (tievel), masculine, Old High German tiuval, tioval, masculine (in the plural, neuter also); corresponding to Old Saxon diuƀal, Dutch duivel, Anglo-Saxon deófol, equivalent to English devil. The West Teutonic words have apparently genuine Teutonic sounds; on account, however, of the equivalent Gothic diabaúlus, Greek-Latin diabolus, it is certain that the word was borrowed. The early existence of the West Teutonic word, attested by the permutation of Low German d to High German t, can only be explained by the assumption that it was introduced into High German in the 5th or 6th century through a Gothic medium (as also taufen, Pfaffe, Kirche, Heide, Samstag, and probably Engel), for the connection of the cognates with Greek-Latin (Ecclesiast.) diabolus cannot be doubted. The genuine High German term for ‘evil spirit’ was Goth unhulþô, Old High German unholda, literally ‘the demons.’