battlement vs outwork

battlement

noun
  • 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. 

  • Any high wall for defense. 

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