constancy vs steadfastness

constancy

noun
  • The quality of being constant; steadiness or faithfulness in action, affections, purpose, etc. 

  • An unchanging quality or characteristic of a person or thing. 

steadfastness

noun
  • Loyalty in the face of trouble and difficulty. 

  • Steadfast resolution. 

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