The Collaborative International Dictionary of English v.0.48:

Inhumanity \In`hu*man"i*ty\, n.; pl. Inhumanities. [L.
   inhumanitas: cf. F. inhumanit['e].]
   The quality or state of being inhuman or inhumane; cruelty;
   barbarity.
   [1913 Webster]

         Man's inhumanity to man
         Makes countless thousands mourn.         --Burns.
   [1913 Webster]

WordNet (r) 3.0 (2006):

inhumanity
    n 1: the quality of lacking compassion or consideration for
         others [syn: inhumaneness, inhumanity] [ant:
         humaneness]
    2: an act of atrocious cruelty [syn: atrocity, inhumanity]