overseer vs slaveowner

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. 

slaveowner

noun
  • Someone who has control or ownership over another human being; the owner of a slave. 

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