bulwark vs shelter

bulwark

verb
  • To provide protection of defense for something. 

  • To fortify something with a wall or rampart. 

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. 

shelter

verb
  • To provide cover from damage or harassment; to shield; to protect. 

  • To take cover. 

noun
  • A refuge, haven or other cover or protection from something. 

  • An institution that provides temporary housing for homeless people, battered women, etc. 

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