defame vs impugn

defame

verb
  • To charge; to accuse (someone) of an offence. 

  • To harm or diminish the reputation of; to disparage. 

  • To disgrace; to bring into disrepute. 

impugn

verb
  • To verbally assault, especially to argue against an opinion, motive, or action; to question the truth or validity of. 

How often have the words defame and impugn occurred in a corpus of books? (source: Google Ngram Viewer )