bulwark vs outwork

bulwark

noun
  • A defensive wall or rampart. 

  • A defense or safeguard. 

  • 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. 

outwork

noun
  • A minor, subsidiary fortification built beyond the main limits of fortification. 

  • Agricultural work done outdoors in the fields. 

verb
  • To work out to a finish; to complete. 

  • To work faster or harder than. 

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