1. (Physical Geography) a loud cracking or deep rumbling noise caused by the rapid expansion of atmospheric gases which are suddenly heated by lightning. 2. any loud booming sound. 3. a violent threat or denunciation. 4. steal someone's thunder to detract from the attention due to another by forestalling him or her. vb. n. 1. The crashing or booming sound produced by rapidly expanding air along the path of the electrical discharge of lightning. 2. A sound that resembles or suggests thunder. v. thun·dered, thun·der·ing, thun·ders. v. intr. 1. a loud, explosive, resounding noise produced by the explosive expansion of air heated by a lightning discharge. 2. any loud, resounding noise: the thunder of applause. 3. to give forth thunder (often used impersonally with it as the subject): It thundered all night. n. 1. The crashing or booming sound produced by rapidly expanding air along the path of the electrical discharge of lightning. 2. A sound that resembles or suggests thunder. v. thun·dered, thun·der·ing, thun·ders. v. intr.
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