disbelief vs pessimism

disbelief

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

  • Astonishment. 

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

pessimism

noun
  • The condition of being pessimal. 

  • A general belief that bad things will happen. 

  • The doctrine that this world is the worst of all possible worlds. 

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