An Etymological Dictionary of the German Language/Annotated/Thor

Thor (1.), masculine, ‘fool,’ from Middle High German tôre, tôr, masculine, ‘insane person, fool’; *tôro, masculine, has not yet been found in Old High German. The r of the adjective has originated in s (z), as is shown by Old High German tusîg, Anglo-Saxon dysig, ‘foolish,’ English dizzy, and Dutch duizelig, ‘dizzy.’ For further Teutonic cognates of the Aryan root dhus (dhaus, dhwē̆s) see under Dusel; it is uncertain whether Latin furere, ‘to rage,’ is derived from this root dhus. —

Thor (2.), neuter, ‘gate, gateway,’ from the equivalent Middle High German and Old High German tor, neuter; corresponding to Gothic daúr, Old Saxon dor, neuter, ‘gate, door.’ See Thür.