gravamen vs virtuality

gravamen

noun
  • A grievance complained of. 

  • The essence or ground of a complaint. 

  • A document sent by the Lower House of Convocation to the Upper House to inform the latter of certain grievances in the church. 

  • The essence or most important aspect of a piece of writing, a point of argument, etc.; the gist. 

virtuality

noun
  • The quality of being virtual; virtualness. 

  • A state of being virtual. 

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