certificate vs word of honor

certificate

noun
  • A document evidencing ownership or debt. 

  • A motion picture age rating. 

  • A document serving as evidence that a person has completed an educational course, issued either by an institution not authorised to grant diplomas, or to a student not qualifying for a diploma. 

  • A document containing a certified statement. 

  • The information needed in order to verify a positive answer to a problem. 

verb
  • To supply with a certificate, especially following certification. 

word of honor

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

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