emissary vs power of attorney

emissary

noun
  • An agent sent on a mission to represent the interests of someone else. 

  • An underground channel by which the water of a lake escapes. 

  • A venous channel in the skull. 

power of attorney

noun
  • A legal document allowing one person to act as the agent of another. 

  • The legal authorisation of one person to act as the agent of another. 

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