Ferocious

google

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mid 17th century: from Latin ferox, feroc- ‘fierce’ + -ious.

wiktionary

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Taken from Latin ferox(“wild, bold, savage, fierce”) (with the suffix -ous), from ferus(“wild, savage, fierce”).

etymonline

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ferocious (adj.)

1640s, from Latin ferocis, oblique case of ferox "fierce, wild-looking," from 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"). Alternative ferocient (1650s) is seldom seen. Related: Ferociously; ferociousness.