compel vs volunteer

compel

verb
  • To force, constrain or coerce. 

  • To exact, extort, (make) produce by force. 

  • To overpower; to subdue. 

volunteer

verb
  • To do or offer to do something voluntarily. 

  • To offer, usually unprompted. 

  • To grow without human sowing or intentional cultivation. 

  • To enlist oneself as a volunteer. 

  • To offer the services of (someone else) to do something. 

noun
  • A plant that grows spontaneously, without being cultivated on purpose; see volunteer plant in Wikipedia. 

  • A voluntary member of the organized militia of a country, as distinguished from a regular or member of the standing army. 

  • One who enters into military service voluntarily (but who, when in service, is subject to discipline and regulations like other soldiers), as opposed to a conscript. 

  • A native or resident of the American state of Tennessee. 

  • One who enters into, or offers themself for, any service of their own free will, especially when done without pay. 

  • A person who acts out of their own will without a legal obligation, such as a donor. 

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