bulwark vs parapet

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. 

parapet

noun
  • A low protective wall. 

  • A fortification consisting of a wall. 

  • Part of a perimeter that extends above the roof. 

  • Hyponym: balustrade 

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