betrothal vs word of honor

betrothal

noun
  • The fact of being betrothed; a mutual promise, engagement, or contract for a future marriage between two people. 

  • The act of betrothing. 

word of honor

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

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