quarterdeck vs sentry

quarterdeck

noun
  • The aft part of the upper deck of a ship; normally reserved for officers 

sentry

noun
  • A guard, particularly on duty at the entrance to a military base. 

  • A animal like a marmot tasked with alerting the pack to danger. 

  • Sentry duty; time spent being a sentry. 

  • A watchtower. 

  • A form of drag to be towed underwater, which on striking bottom is upset and rises to the surface. 

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