apology vs bulwark

apology

noun
  • A formal justification, defence. 

  • An expression of remorse or regret for having said or done something that harmed another: an instance of apologizing (saying that one is sorry). 

  • Anything provided as a substitute; a makeshift. 

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. 

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