Image via WikipediaO.E. þunor, from P.Gmc. *thunraz (cf. O.N. þorr, O.Fris. thuner, M.Du. donre, Du. donder, O.H.G. donar, Ger. Donner "thunder"), from PIE *(s)tene- "to resound, thunder" (cf. Skt. tanayitnuh "thundering," Pers. tundar "thunder," L. tonare "to thunder"). Swed. tordön is lit. "Thor's din." The intrusive -d- is also found in Du. and Icelandic versions of the word. The verb is O.E. þunrian; fig. sense of "to speak loudly, threateningly, bombastically" is recorded from c.1340. Thunderbolt is from c.1440; thunderclap is from c.1386; thunderstruck is from 1613, originally fig.; the lit. sense always has been rare. Thunderhead "high-piled cloud" is recorded from 1861.