cosigner vs mainstay

cosigner

noun
  • A person who accepts joint responsibility for the debt of another 

  • A cosignatory 

mainstay

noun
  • 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. 

  • A chief support. 

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