know vs vouch

know

verb
  • To perceive the truth or factuality of; to be certain of or that. 

  • To experience. 

  • To understand or have a grasp of through experience or study. 

  • To be or become aware or cognizant. 

  • To be able to play or perform (a song or other piece of music). 

  • To be acquainted or familiar with; to have encountered. 

  • To be aware of; to be cognizant of. 

  • To recognize as the same (as someone or something previously encountered) after an absence or change. 

  • To have knowledge; to have information, be informed. 

noun
  • Knowledge; the state of knowing. 

  • Knowledge; the state of knowing; now confined to the fixed phrase ‘in the know’ 

vouch

verb
  • To express confidence in or take responsibility for (the correctness or truth of) something. 

  • To assert, aver, or declare (something). 

  • To provide evidence or proof. 

  • To back, confirm, or support (someone or something) with credible evidence or proof. 

  • To call on (someone) to be a witness to something. 

  • To affirm or warrant the correctness or truth of (something); also, to affirm or warrant (the truth of an assertion or statement). 

  • To bear witness or testify; to guarantee or sponsor. 

  • To cite or rely on (an authority, a written work, etc.) in support of one's actions or opinions. 

  • To bear witness or testify to the nature or qualities (of someone or something). 

  • In full vouch to warrant or vouch to warranty: to summon (someone) into court to establish a warranty of title to land. 

  • Followed by over: of a vouchee (a person summoned to court to establish a warranty of title): to summon (someone) to court in their place. 

noun
  • An assertion, a declaration; also, a formal attestation or warrant of the correctness or truth of something. 

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