Synonyms for Cruelty (same or very similar meaning)
WordNet sense 1 (feelings of extreme heartlessness):
mercilessness, pitilessness, ruthlessnessWordNet sense 2 (the quality of being cruel and causing tension or annoyance):
cruelness, harshnessWordNet sense 3 (a cruel act; a deliberate infliction of pain and suffering):
inhuman treatmentFrom the ODE community, based on WordNetadd/edit