author vs ghostwrite

author

verb
  • To create a work as its author. 

noun
  • Someone who writes books for a living. 

  • The originator or creator of a work, especially of a literary composition. 

ghostwrite

verb
  • To author a literary work or speech in the place of another. 

  • To write under the name of another (especially literary works). 

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