outwork vs parapet

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. 

parapet

noun
  • A fortification consisting of a wall. 

  • Part of a perimeter that extends above the roof. 

  • A low protective wall. 

  • Hyponym: balustrade 

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