mainstay vs proponent

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. 

proponent

noun
  • One who supports something; an advocate 

  • One who makes a proposal or proposition. 

  • One who propounds a will for probate. 

adj
  • Making proposals; proposing. 

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