brontē

Thunder is one of the few words in the New Testament that almost never means only weather. Israel's oldest memory of meeting God was a storm on a mountain: fire, smoke, a shaking peak, and thunder overhead. Once that scene was fixed in the imagination, the sound itself became shorthand for God showing up, and the writers use it that way.

That is why one plain word can do such different jobs. In Revelation it turns up again and again in a fixed cluster of storm signs, lightning and voices (φωνή) and thunder, sometimes with an earthquake or hail added: the writer is not forecasting weather but telling the reader that heaven has opened and God is acting. When something is said to sound like thunder, the comparison is about authority as much as volume, because thunder is the noise the sky makes when God speaks. And in one strange scene the thunders do the speaking: seven of them say words John could have written down, until he is told to seal them up.

The one everyday use points the same direction. In John 12:29 a crowd hears a voice from heaven and concludes it must have thundered. The mistake only works because thunder was exactly what people expected the voice of God to sound like. Hebrew makes the overlap plainer still: alongside its own noun for thunder (רַעַם) it uses its ordinary word for voice (קוֹל) of the same sound, so that in Psalm 29 the voice of the LORD over the waters and a thunderclap are one and the same thing.

Mark uses the word once outside all of this, in a nickname. He calls James and John "sons of thunder", a way of naming people by what they resemble.