mainstay vs strength

mainstay

noun
  • A chief support. 

  • Someone or something that can be depended on to make a regular contribution. 

  • A stabilising rope from the top of the mainmast to the bottom of the foremast. 

strength

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

  • The intensity of a force or power; potency. 

  • The quality or degree of being strong. 

  • A positive attribute. 

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