caution vs warn

caution

verb
  • To warn; to alert, advise that caution is warranted. 

  • To give a yellow card 

noun
  • A formal warning given as an alternative to prosecution in minor cases. 

  • Security; guaranty; bail. 

  • A yellow card. 

  • Prudence when faced with, or when expecting to face, danger; care taken in order to avoid risk or harm. 

  • A careful attention to the probable effects of an act, in order that failure or harm may be avoided. 

warn

verb
  • To give warning. 

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

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

  • 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 caution and warn occurred in a corpus of books? (source: Google Ngram Viewer )