slanderer       
noun [ C ] uk/ˈslɑːn.dər.ər/ us/ˈslæn.dɚ.ɚ/
 诽谤、诋毁他人的人
a person who slanders someone (= damages their reputation by making a false spoken statement about them)
  I described him as a serial slanderer who poisoned political debate. 我认为他习惯性地诋毁他人来破坏政治辩论。 
 The documents prove that they are liars and deliberate slanderers of my name. 这些文件证明他们说了谎,对我的名声进行了蓄意诽谤。 
 See: slander
 - More examples
 - The slanderer would be free to leave court and slander again if he likes.
 - She shows her anger towards him, referring to him as a “contemptible slanderer.”
 - Knowing that the accusations were untrue, he did not consider it necessary to respond to his slanderer.