Etymology

The d in thunder is epenthetic, and is not found in Modern Dutch donder, from earlier d-less Old English þunor, Middle Dutch donre, together with Old Norse þorr, Old Frisian þuner, Old High German donar descended from Proto-Germanic *þunraz, built on a PIE stem *(s)tene- also found in Sanskrit tana-itnu- "thundering", Latin tonare "to thunder" (see also tornado).