incumbent vs principal

incumbent

adj
  • Prevalent, prevailing, predominant. 

  • Lying; resting; reclining; recumbent. 

  • Being the current holder of an office or a title. 

  • Imposed on someone as an obligation, especially due to one's office. 

  • Resting on something else; in botany, said of anthers when lying on the inner side of the filament, or of cotyledons when the radicle lies against the back of one of them 

  • Bent downwards so that the ends touch, or rest on, something else. 

noun
  • The current holder of an office, such as ecclesiastical benefice or an elected office. 

  • A holder of a position as supplier to a market or market segment that allows the holder to earn above-normal profits. 

principal

adj
  • Primary; most important; first level in importance. 

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

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 

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