mainstay vs opponent

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. 

opponent

noun
  • The participant who opens an academic debate by putting forward objections to a theological or philosophical thesis. 

  • One who opposes another; one who works or takes a position against someone or something; one who attempts to stop the progress of someone or something. 

  • One who opposes another in words (in a dispute, argument or controversy). 

  • One who is opposed or objects (to a policy, course of action or set of ideas). 

  • One who opposes another physically (in a fight, sport, game, or competition). 

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