inconstancy vs perfidy

inconstancy

noun
  • Lack of constancy; lack of consistency in thought, emotion or action. 

perfidy

noun
  • A state or act of violating faith or allegiance; violation of a promise or vow, or of trust 

  • Specifically, in warfare, an illegitimate act of deception, such as using symbols like the Red Cross or white flag in a false claim of surrender to gain proximity to an enemy for purposes of attack. 

  • A state or act of deceit. 

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