An Etymological Dictionary of Astronomy and Astrophysics

A loud rumbling sound emitted by rapidly expanding air along the path of the electrical discharge of lightning.

Etymology (EN): M.E. thonder, thunder, O.E. thunor, from P.Gmc. *thunraz (cf. O.Fris. thuner, M.Du. donre, Du. donder, O.H.G. donar, Ger. Donner “thunder”), cognate with Pers. tondar, as below.

Etymology (PE): Tondar; Mid.Pers. tndwr, Sogdian twntr; cf. Skt. stan- “to thunder, resound,” tanyati “thunders, roars,” tanyu- “thundering,” stanatha- “thunder;” L. tonare “to thunder,” tonitrus “thunder” (Fr. tonnerre); PIE base *(s)tene- “to resound, thunder.”