atrocity (n.)
1530s, from Middle French atrocité or directly from Latin atrocitatem (nominative atrocitas) "cruelty, fierceness, harshness," noun of quality from atrox "fierce, cruel, frightful," from PIE *atro-ek-, from root *ater- "fire" (see atrium) + *okw- "see" (see eye (n.)); thus "of fiery or threatening appearance." The meaning "an atrocious deed" is from 1793.