certificate vs testimonial

certificate

noun
  • A document containing a certified statement. 

  • 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. 

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

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

testimonial

noun
  • A tribute given in appreciation of someone's service etc. 

  • A statement, especially one given under oath; testimony 

  • A match played in tribute to a particular player (who sometimes receives a proportion of the gate money). 

  • A written recommendation of someone's worth or character 

adj
  • Serving as testimony. 

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