director vs principal

director

noun
  • A member of a board of directors. 

  • A device that displays graphical information concerning the targets of a weapons system in real time. 

  • A counselor, confessor, or spiritual guide. 

  • The common axis of symmetry of the molecules of a liquid crystal. 

  • That which directs or orientates something. 

  • One who directs; the person in charge of managing a department or directorate (e.g., director of engineering), project, or production (as in a show or film, e.g., film director). 

principal

noun
  • The chief administrator of a school. 

  • A diapason, a type of organ stop on a pipe organ. 

  • The construction that gives shape and strength to a roof, generally a truss of timber or iron; or, loosely, the most important member of a piece of framing. 

  • A dancer at the highest rank within a professional dance company, particularly a ballet company. 

  • The primary participant in a crime. 

  • The first two long feathers of a hawk's wing. 

  • A security principal. 

  • A legal person that authorizes another (the agent) to act on their behalf; or on whose behalf an agent or gestor in a negotiorum gestio acts. 

  • The chief executive and chief academic officer of a university or college. 

  • The money originally invested or loaned, on which basis interest and returns are calculated. 

  • A partner or owner of a business. 

  • One of the turrets or pinnacles of waxwork and tapers with which the posts and centre of a funeral hearse were formerly crowned 

adj
  • Chosen or assumed among a branch of possible values of a multi-valued function so that the function is single-valued. 

  • Primary; most important; first level in importance. 

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