WordWeb Online

1. (used of statements) harmful and often untrue; tending to discredit or malign
   "John did not delight in denigrating his opponent";
   - calumniatory, calumnious, defamatory, denigrative, denigratory, libellous, libelous [US], slanderous

1. Cause to seem less serious; play down
   "Don't denigrate his influence";
   - minimize, belittle, derogate, minimise [Brit]
    
2. Charge falsely or with malicious intent; attack the good name and reputation of someone
   - defame, slander, smirch, asperse, calumniate, smear, sully, besmirch

See also: harmful

Type of: accuse, belittle, charge, disparage, pick at