ferocity (n.)

c. 1600, from French férocité, from Latin ferocitatem (nominative ferocitas) "fierceness," from ferocis, oblique case of ferox "bold, courageous, warlike; fierce, savage, headstrong, cruel," literally "wild-looking," a derivative of ferus "wild" (from PIE root *ghwer- "wild beast") + -ox (genitive -ocis), a suffix meaning "looking or appearing" (cognate with Greek ōps "eye, sight;" from PIE root *okw- "to see").