erasure vs helotism

erasure

noun
  • A tendency to ignore or conceal an element of society. 

  • The state of having been erased; total blankness. 

  • The action of erasing; deletion; obliteration. 

  • The place where something has been erased. 

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 

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