bulwark vs guardian

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. 

guardian

noun
  • Someone who guards, watches over, or protects. 

  • A superior in a Franciscan monastery. 

  • A person legally responsible for a minor (in loco parentis). 

  • A person legally responsible for an incompetent person. 

  • A major or final enemy; boss. 

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