pervert

Concise Oxford English Dictionary © 2008 Oxford University Press:
pervert

▶verb /pəˈvəːt/ 

• 1 alter from its original meaning or state to a corruption of what was first intended.

• 2 lead away from what is right, natural, or acceptable.

▶noun /ˈpəːvəːt/ a person with abnormal or unacceptable sexual behaviour.

– derivatives
perverter noun.

– origin ME: from OFr. pervertir, from L. pervertere, from per- ‘thoroughly, to ill effect’ + vertere ‘to turn’.