helotism vs thrall

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 

thrall

noun
  • One who is enslaved or under mind control. 

  • The state of being under the control of another person. 

  • A shelf; a stand for barrels, etc. 

verb
  • To make a thrall; enslave. 

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