overseer vs slave-driver

overseer

noun
  • The manager of a plantation of slaves. 

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

slave-driver

noun
  • An overseer of slaves at work; a person who puts slaves to work. 

  • An employer who demands excessive amounts of work from employees. 

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