invigilator vs overseer

invigilator

noun
  • A person who supervises students during an examination; a proctor 

overseer

noun
  • An officer responsible for the care of the poor, making out lists of voters and those who had not paid taxes, etc. 

  • The manager of a plantation of slaves. 

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