apparition vs illusion

apparition

noun
  • An unexpected, wonderful, or preternatural appearance; especially something such as a ghost or phantom. 

  • The first appearance of a star or other luminary after having been invisible or obscured; opposed to occultation. 

  • A period of consecutive days or nights when a particular celestial body may be observed, beginning with the heliacal rising of the body and ending with its heliacal setting. 

  • An act of becoming visible; appearance; visibility. 

  • The thing appearing; a visible object; a form. 

illusion

noun
  • Anything that seems to be something that it is not. 

  • A misapprehension; a belief in something that is in fact not true. 

  • A magician’s trick. 

  • The state of being deceived or misled. 

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