A sudden loud sound of thunder that happens immediately after a lightning strike, or any sudden surprising event or noise.
Combination of 'thunder' (from Old English thunor, the Norse god of thunder) and 'clap' (from Middle English clapthe, meaning to strike). The phrase literally describes the striking sound that accompanies lightning.
Thunder is actually silent—the lightning creates a shockwave in the air that reaches your ears as the explosive 'clap.' When you see lightning and count the seconds before hearing thunder, you're measuring how far away the lightning struck because sound travels so much slower than light!
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