Old English þunor, from Proto-Germanic *thunraz (cf. Old Norse þorr, Old Frisian thuner, Middle Dutch donre, Dutch donder, Old High German donar, German Donner "thunder"), from PIE *(s)tene- "to resound, thunder" (cf. Sanskrit tanayitnuh "thundering," Persian tundar "thunder," Latin tonare "to thunder"). Swedish tordön is literally "Thor's din." The intrusive -d- is also found in Dutch and Icelandic versions of the word.