babysitter vs observer

babysitter

noun
  • A person who cares for one or more babies or children for a short period of time in place of their legal guardians. 

observer

noun
  • One who adheres or follows laws, guidelines, etc. 

  • One who makes observations, monitors or takes notice 

  • A crew member on an aircraft who makes observations of enemy positions or aircraft 

  • A person sent as a representative, to a meeting or other function to monitor but not to participate 

  • A country or other entity which has limited participation rights within an organization. 

  • A sentry etc. manning an observation post 

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