Is or was ピカドン used for lightning and thunder? I've read that (onomatopoeia for a flash and for a loud bang) is used for atomic bombs, but is it, or was it prior to Hiroshima, used to describe the flash of lightning and the sound of thunder?

Both and / were (and still are) fairly common and generic onomatopoeias. existed before WWII (confirmed on ).

If I understand correctly, their combination, , specifically referred to atomic bombs. It originated from onomatopoeias, but itself is a noun.