impair vs ravage

impair

verb
  • To weaken; to affect negatively; to have a diminishing effect on. 

ravage

verb
  • To devastate or destroy something. 

  • To have vigorous sexual intercourse with. 

  • To pillage or sack something, to lay waste to something. 

  • To rape. 

  • To wreak destruction. 

noun
  • Depredation or devastation. 

  • Grievous damage or havoc. 

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