The Collaborative International Dictionary of English v.0.48:

Thunder \Thun"der\, n. [OE. [thorn]under, [thorn]onder,
   [thorn]oner, AS. [thorn]unor; akin to [thorn]unian to
   stretch, to thunder, D. donder thunder, G. donner, OHG.
   donar, Icel. [thorn][=o]rr Thor, L. tonare to thunder,
   tonitrus thunder, Gr. to`nos a stretching, straining, Skr.
   tan to stretch. [root]52. See Thin, and cf. Astonish,
   Detonate, Intone, Thursday, Tone.]
   1. The sound which follows a flash of lightning; the report
      of a discharge of atmospheric electricity.
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   2. The discharge of electricity; a thunderbolt. [Obs.]
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            The revenging gods
            'Gainst parricides did all their thunders bend.
                                                  --Shak.
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   3. Any loud noise; as, the thunder of cannon.
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   4. An alarming or statrling threat or denunciation.
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            The thunders of the Vatican could no longer strike
            into the heart of princes.            --Prescott.
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   Thunder pumper. (Zool.)
      (a) The croaker (Haploidontus grunniens).
      (b) The American bittern or stake-driver.

   Thunder rod, a lightning rod. [R.]

   Thunder snake. (Zool.)
      (a) The chicken, or milk, snake.
      (b) A small reddish ground snake (Carphophis amoena syn.
          Celuta amoena) native to the Eastern United States;
          -- called also worm snake.

   Thunder tube, a fulgurite. See Fulgurite.
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