Thun"der*ing*ly

from The Collaborative International Dictionary of English v.0.48

Thundering \Thun"der*ing\, a.
   1. Emitting thunder.
      [1913 Webster]

            Roll the thundering chariot o'er the ground. --J.
                                                  Trumbull.
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   2. Very great; -- often adverbially. [Slang]
      [1913 Webster] -- {Thun"der*ing*ly}, adv.
      [1913 Webster]