countersign vs underwrite

countersign

verb
  • To sign on the opposite side of (a document). 

  • To add a second signature to a document, affirming the validity of the signature of another person. 

noun
  • A second signature added to a document to affirm the validity of the signature of the first person. 

  • The response to a sign or signal. 

underwrite

verb
  • To sign; to put one's name to. 

  • To support, lend support to, guarantee the basis of. 

  • To agree to pay by signing one's name; subscribe. 

  • Specifically, to assume financial responsibility for something, and guarantee it against failure. 

  • To act as an underwriter. 

  • To write below or under; subscribe. 

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