delusion delusion /dɪˈluːʒən/

noun

1. The act of deluding; deception by creating illusory ideas  ( delusion , head game , illusion )
   the act of deluding; deception by creating illusory ideas
    The magician's act ended with an impressive illusion that left everyone in awe.
   The magician's act ended with an impressive illusion that left everyone in awe.
   
   
2. A mistaken or unfounded opinion or idea  ( delusion , hallucination )
   a mistaken or unfounded opinion or idea
    He has delusions of competence
   he has delusions of competence
    His dreams of vast wealth are a hallucination
   his dreams of vast wealth are a hallucination
   
3. (psychology) an erroneous belief that is held in the face of evidence to the contrary  ( delusion , psychotic belief )
   (psychology) an erroneous belief that is held in the face of evidence to the contrary