single-hearted vs steadfast

single-hearted

adj
  • Devoted; unambivalent and dedicated. 

  • Having an honest heart; straightforward, free from duplicity. 

steadfast

adj
  • Firmly loyal or constant; unswerving. 

  • Fixed or unchanging; steady. 

How often have the words single-hearted and steadfast occurred in a corpus of books? (source: Google Ngram Viewer )