severity vs strength

severity

noun
  • The degree of something undesirable; badness or seriousness. 

  • The state of being severe. 

strength

noun
  • The intensity of a force or power; potency. 

  • The quality or degree of being strong. 

  • The strongest part of something; that on which confidence or reliance is based. 

  • A positive attribute. 

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