assistant vs ghost writer

assistant

adj
  • Helping; lending aid or support; auxiliary. 

  • Having a subordinate or auxiliary position. 

noun
  • A software tool that provides assistance in some task, a wizard program. 

  • Sales assistant. 

  • A person who assists or helps someone else. 

ghost writer

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