strengthen vs vitiate

strengthen

verb
  • To empower; to give moral strength to; to encourage; to enhearten. 

  • To make strong or stronger; to add strength to; to increase the strength of; to fortify. 

  • To reinforce, to add to, to support (someone or something) 

  • To grow strong or stronger. 

  • To substantiate; to corroborate (a belief, argument, etc.) 

  • To augment; to improve; to intensify. 

vitiate

verb
  • To debase or morally corrupt. 

  • To make something ineffective, to invalidate. 

  • To spoil, make faulty; to reduce the value, quality, or effectiveness of something. 

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