The Collaborative International Dictionary of English v.0.48:

Barbarity \Bar*bar"i*ty\, n.; pl. Barbarities. [From
   Barbarous.]
   1. The state or manner of a barbarian; lack of civilization.
      [1913 Webster]

   2. Cruelty; ferociousness; inhumanity.
      [1913 Webster]

            Treating Christians with a barbarity which would
            have shocked the very Moslem.         --Macaulay.
      [1913 Webster]

   3. A barbarous or cruel act.
      [1913 Webster]

   4. Barbarism; impurity of speech. [Obs.] --Swift.
      [1913 Webster]

WordNet (r) 3.0 (2006):

barbarity
    n 1: the quality of being shockingly cruel and inhumane [syn:
         atrocity, atrociousness, barbarity, barbarousness,
         heinousness]
    2: a brutal barbarous savage act [syn: brutality, barbarity,
       barbarism, savagery]

Moby Thesaurus II by Grady Ward, 1.0:

73 Moby Thesaurus words for "barbarity":
   Gothicism, Neanderthalism, acuteness, animality, atrociousness,
   atrocity, barbarism, barbarousness, beastliness, bestiality,
   bloodiness, bloodlust, bloodthirst, bloodthirstiness,
   bloody-mindedness, brutality, brutalness, brutishness, cannibalism,
   cruelness, cruelty, destructiveness, extremity, ferociousness,
   ferocity, fiendishness, fierceness, force, furiousness, harshness,
   heartlessness, ill breeding, impetuosity, impoliteness, incivility,
   inclemency, inhumaneness, inhumanity, intensity, malignity,
   mercilessness, mindlessness, murderousness, philistinism,
   pitilessness, rigor, roughness, ruthlessness, sadism,
   sadistic cruelty, sanguineousness, savagery, savagism, severity,
   sharpness, terrorism, troglodytism, truculence, uncivilizedness,
   uncouthness, uncultivatedness, uncultivation, unculturedness,
   ungentleness, unrefinement, vandalism, vehemence, venom,
   viciousness, violence, virulence, wanton cruelty, wildness