1. [adj]  extraordinarily big or impressive; "a thundering success"; "the thundering silence of what was left unsaid"
2. [adj]  sounding like thunder; "the thundering herd"

THUNDERING is a 10 letter word that starts with T.

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

2. \Thun"der*ing\, n.
   Thunder. --Rev. iv. 5.