slanderous

1. Given or disposed to slander; uttering slander. «Slanderous tongue.» Shak.

2. Embodying or containing slander; calumnious; as, slanderous words, speeches, or reports.

-- Slan·der·ous·ly, adv. -- Slan·der·ous·ness, n.

adjective

Damaging to the reputation: calumnious, defamatory, detractive, injurious, invidious, scandalous. Law libelous. See attack/defend, crimes, law.

The adjective has one meaning:

Meaning #1: (used of statements) harmful and often untrue; tending to discredit or malign
  Synonyms: calumniatory, calumnious, defamatory, denigrative, denigrating, denigratory, libellous, libelous