bastion vs freeboard

bastion

noun
  • A projecting part of a rampart or other fortification. 

  • A well-fortified position; a stronghold or citadel. 

  • A person, group, or thing, that strongly defends some principle. 

  • Any large prominence; something that resembles a bastion in size and form. 

verb
  • To furnish with a bastion. 

freeboard

noun
  • The distance between a water level and the top of something that contains or restrains it (such as a dam). 

  • The distance between the top of sea ice and the water level. 

  • A type of skateboard which simulates the movement of a snowboard when used on a downhill coarse, allowing snowboarding techniques, which has an addition of two centerline casters that extend below the traditional skateboard wheels and bogies. 

  • The vertical distance between the waterline and the uppermost watertight deck of a vessel. 

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