adherence vs steadfastness

adherence

noun
  • Faithful support for some cause. 

  • An extent to which a patient continues an agreed treatment plan. 

  • The fulfilment of the legal obligation of residing with wife or husband. 

  • A close physical union of two objects. 

steadfastness

noun
  • Loyalty in the face of trouble and difficulty. 

  • Steadfast resolution. 

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