The Collaborative International Dictionary of English v.0.48:

Ferocity \Fe*roc"i*ty\, n. [L. ferocitas, fr. ferox, -ocis,
   fierce, kin to ferus wild: cf. F. ferocit['e]. See Fierce.]
   Savage wildness or fierceness; fury; cruelty; as, ferocity of
   countenance.
   [1913 Webster]

         The pride and ferocity of a Highland chief. --Macaulay.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ferocity
    n 1: the property of being wild or turbulent; "the storm's
         violence" [syn: ferocity, fierceness, furiousness,
         fury, vehemence, violence, wildness]

Moby Thesaurus II by Grady Ward, 1.0:

56 Moby Thesaurus words for "ferocity":
   aggression, aggressiveness, animality, antagonism, atrociousness,
   barbarity, barbarousness, beastliness, bellicism, bellicosity,
   belligerence, belligerency, bestiality, bloodiness, bloodlust,
   bloodthirst, bloodthirstiness, bloody-mindedness, brutality,
   brutalness, brutishness, cannibalism, chauvinism, combativeness,
   contentiousness, cruelness, cruelty, ferociousness, fiendishness,
   fierceness, fight, hostility, inhumaneness, inhumanity, jingoism,
   martialism, militancy, militarism, pugnaciousness, pugnacity,
   quarrelsomeness, ruthlessness, saber rattling, sadism,
   sadistic cruelty, sanguineousness, savagery, truculence,
   unfriendliness, unpeacefulness, vandalism, viciousness, violence,
   wanton cruelty, warmongering, warpath