delusion in WordNet English dictionary

1. the act of deluding; deception by creating illusory ideas
   delusion  illusion  head game 
   
2. a mistaken or unfounded opinion or idea
   "he has delusions of competence"; "his dreams of vast wealth are a hallucination"
   delusion  hallucination 
   
3. (psychology) an erroneous belief that is held in the face of evidence to the contrary
   delusion  psychotic belief