promissory note vs word of honor

promissory note

noun
  • A document saying that someone owes a specific amount of money to someone else, often with the deadline and interest fees; the primary purposes of a promissory note are to evidence the debt obligation incurred, and to establish terms for payment thereof. 

word of honor

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

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