battlement vs freeboard

battlement

noun
  • Any high wall for defense. 

  • In fortification: an indented parapet, formed by a series of rising members called cops or merlons, separated by openings called crenelles or embrasures, the soldier sheltering himself behind the merlon while he fires through the embrasure or through a loophole in the battlement. 

  • The towering roof of heaven. 

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 battlement and freeboard occurred in a corpus of books? (source: Google Ngram Viewer )