fidelity vs steadfastness

fidelity

noun
  • Loyalty to one's spouse or partner, including abstention from cheating or extramarital affairs. 

  • Accuracy, or exact correspondence to some given quality or fact. 

  • Faithfulness to one's duties. 

  • The degree to which a system accurately reproduces an input. 

steadfastness

noun
  • Loyalty in the face of trouble and difficulty. 

  • Steadfast resolution. 

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