controvert vs oppugn

controvert

verb
  • To argue against (something or someone); to contradict, to deny. 

  • To dispute, to argue about (something). 

  • To be involved or engaged in controversy; to argue. 

oppugn

verb
  • To contradict or controvert; to oppose; to challenge or question the truth or validity of a given statement. 

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