countermand vs warn

countermand

verb
  • To counteract, to act against, to frustrate. 

  • To recall a person or unit with such an order. 

  • To revoke (a former command); to cancel or rescind by giving an order contrary to one previously given. 

  • To cancel an order for (some specified goods). 

noun
  • An order to the contrary of a previous one. 

warn

verb
  • To caution or admonish (someone) against unwise or unacceptable behaviour. 

  • To notify or inform (someone, about something). 

  • To give warning. 

  • To summon (someone) to or inform of a formal meeting or duty. 

  • To advise or order to go or stay away. 

  • To make (someone) aware of impending danger, evil, etc. 

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