bulwark vs caution

bulwark

noun
  • A defense or safeguard. 

  • A defensive wall or rampart. 

  • A breakwater. 

  • Any means of defence or security. 

  • The planking or plating along the sides of a nautical vessel above her gunwale that reduces the likelihood of seas washing over the gunwales and people being washed overboard. 

verb
  • To fortify something with a wall or rampart. 

  • To provide protection of defense for something. 

caution

noun
  • Security; guaranty; bail. 

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

  • 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. 

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

  • To give a yellow card 

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