promise vs word of honor

promise

noun
  • an oath or affirmation; a vow 

  • A transaction between two persons whereby the first person undertakes in the future to render some service or gift to the second person or devotes something valuable now and here to his use. 

  • A placeholder object representing the eventual result of an asynchronous operation. 

  • Reason to expect improvement or success; potential. 

verb
  • To commit to (some action or outcome), or to assure (a person) of such commitment; to make an oath or vow. 

  • To give grounds for expectation, especially of something good. 

word of honor

noun
  • A promise, or a pledge of one's good faith. 

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