permission vs power of attorney

permission

noun
  • authorisation; consent (especially formal consent from someone in authority) 

  • The act of permitting. 

  • Flags or access control lists pertaining to a file that dictate who can access it, and how. 

verb
  • To grant or obtain authorization for. 

power of attorney

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

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

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