Source : Webster's Revised Unabridged Dictionary (1913)

Tempestuous \Tem*pes"tu*ous\, a. [L. tempestuous: cf. OF.
   tempestueux, F. temp[^e]tueux.]
   Of or pertaining to a tempest; involving or resembling a
   tempest; turbulent; violent; stormy; as, tempestuous weather;
   a tempestuous night; a tempestuous debate. --
   {Tem*pes"tu*ous*ly}, adv. -- {Tem*pes"tu*ous*ness}, n.

         They saw the Hebrew leader, Waiting, and clutching his
         tempestuous beard.                       --Longfellow.

Source : WordNet®

tempestuousness
     n : a state of wild storminess