The Collaborative International Dictionary of English v.0.48:

Thunderous \Thun"der*ous\, a. [Written also thundrous.]
   1. Producing thunder. [R.]
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            How he before the thunderous throne doth lie.
                                                  --Milton.
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   2. Making a noise like thunder; sounding loud and deep;
      sonorous.
      [1913 Webster] -- Thun"der*ous*ly, adv.
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