disbelief vs irreligion

disbelief

noun
  • Unpreparedness, unwillingness, or inability to believe that something is the case. 

  • Astonishment. 

  • The loss or abandonment of a belief; cessation of belief. 

irreligion

noun
  • The state of being irreligious; irreligious sentiment or thought. 

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