Source : Webster's Revised Unabridged Dictionary (1913)

Ferocious \Fe*ro"cious\, a. [L. ferox, -ocis, fierce: cf. F.
   f['e]roce. See {Ferocity}.]
   Fierce; savage; wild; indicating cruelty; ravenous;
   rapacious; as, ferocious look or features; a ferocious lion.

         The humbled power of a ferocious enemy.  --Lowth.

   Syn: {Ferocious}, {Fierce}, {Savage}, {Barbarous}.

   Usage: When these words are applied to human feelings or
          conduct, ferocious describes the disposition; fierce,
          the haste and violence of an act; barbarous, the
          coarseness and brutality by which it was marked;
          savage, the cruel and unfeeling spirit which it
          showed. A man is ferocious in his temper, fierce in
          his actions, barbarous in the manner of carrying out
          his purposes, savage in the spirit and feelings
          expressed in his words or deeds. -- {Fe*ro"cious*ly},
          adv. -- {Fe*ro"cious*ness}, n.

                It [Christianity] has adapted the ferociousness
                of war.                           --Blair.

Source : WordNet®

ferociousness
     n : the trait of extreme cruelty [syn: {brutality}, {viciousness},
          {savageness}, {savagery}]