severity vs stiffness

severity

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

  • The state of being severe. 

stiffness

noun
  • inelegance; a lack of relaxedness. 

  • rigidity or a measure of rigidity. 

  • inflexibility or a measure of inflexibility. 

  • muscular tension due to unaccustomed or excessive exercise or work; soreness. 

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