helotism vs slavery

helotism

noun
  • The permanent oppression of a nominally free group of people 

  • A form of mutualism in which one species is forced to perform tasks for another, for their mutual benefit 

slavery

noun
  • A condition of servitude endured by a slave. 

  • A condition in which one is captivated or subjugated, as by greed or drugs. 

  • An institution or social practice of owning human beings as property, especially for use as forced laborers. 

  • Forced labor in general, regardless of legality. 

adj
  • Covered in slaver; slobbery. 

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