credo vs unbelief

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. 

unbelief

noun
  • An absence (or rejection) of belief, especially religious belief 

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