oath vs word of honor

oath

noun
  • A solemn pledge or promise that invokes a deity, a ruler, or another entity (not necessarily present) to attest the truth of a statement or sincerity of one's desire to fulfill a contract or promise. 

  • A light, irreverent or insulting appeal to a deity or other entity. 

  • A curse, a curse word. 

  • A statement or promise which is strengthened (affirmed) by such a pledge. 

word of honor

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

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