credo vs nonbelief

credo

noun
  • A statement of a belief or a summary statement of a whole belief system; also (metonymically) the belief or belief system itself. 

  • The liturgical creed (usually the Nicene Creed), or a musical arrangement of it for use in church services. 

nonbelief

noun
  • Failure to believe; lack of belief. 

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