seriousness vs stiffness

seriousness

noun
  • The state or quality of being serious. 

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 seriousness and stiffness occurred in a corpus of books? (source: Google Ngram Viewer )