vicious

Concise Oxford English Dictionary © 2008 Oxford University Press:
vicious/ˈvɪʃəs/

▶adjective

• 1 cruel or violent.

  ■ (of an animal) wild and dangerous.

• 2 literary immoral.

• 3 archaic (of language or reasoning) imperfect; defective.

– derivatives
viciously adverb,
viciousness noun.

– origin ME: from OFr. vicious or L. vitiosus, from vitium ‘vice’.