illness vs strength

illness

noun
  • An instance of a disease or poor health. 

  • A state of bad health or disease. 

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 illness and strength occurred in a corpus of books? (source: Google Ngram Viewer )