The Collaborative International Dictionary of English v.0.48:

Cruelty \Cru"el*ty\ (-t[y^]), n.; pl. Cruelties (-t[i^]z).
   [OF. cruelt['e], F. cruaut['e], fr. L. crudelitas, fr.
   crudelis. See Cruel.]
   [1913 Webster]
   1. The attribute or quality of being cruel; a disposition to
      give unnecessary pain or suffering to others; inhumanity;
      barbarity.
      [1913 Webster]

            Pierced through the heart with your stern cruelty.
                                                  --Shak.
      [1913 Webster]

   2. A cruel and barbarous deed; inhuman treatment; the act of
      willfully causing unnecessary pain.
      [1913 Webster]

            Cruelties worthy of the dungeons of the Inquisition.

            Macaulay.
      [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

52 Moby Thesaurus words for "cruelty":
   animality, atrociousness, atrocity, barbarity, barbarousness,
   beastliness, bestiality, bloodiness, bloodlust, bloodthirst,
   bloodthirstiness, bloody-mindedness, brutality, brutalness,
   brutishness, cannibalism, cruelness, ferociousness, ferocity,
   fiendishness, fierceness, flintiness, hardness, harshness,
   heartlessness, inclemency, inexorableness, inhumaneness,
   inhumanity, mercilessness, pitilessness, relentlessness,
   remorselessness, ruthlessness, sadism, sadistic cruelty,
   sanguineousness, savagery, short shrift, tender mercies,
   truculence, uncompassionateness, unfeelingness, unforgivingness,
   unmercifulness, unremorsefulness, unsympatheticness,
   unyieldingness, vandalism, viciousness, violence, wanton cruelty