Source : Webster's Revised Unabridged Dictionary (1913)

Atrocity \A*troc"i*ty\, n.; pl. {Atrocities}. [F. atrocit['e],
   L. atrocitas, fr. atrox, atrocis, cruel.]
   1. Enormous wickedness; extreme heinousness or cruelty.

   2. An atrocious or extremely cruel deed.

            The atrocities which attend a victory. --Macaulay.

Source : WordNet®

atrocity
     n 1: the quality of being shockingly cruel and inhumane [syn: {atrociousness},
           {barbarity}, {barbarousness}, {heinousness}]
     2: an act of atrocious cruelty [syn: {inhumanity}]