delusion

(noun) (psychology) an erroneous belief that is held in the face of evidence to the contrary. Synonyms: psychotic belief.

(noun) a mistaken or unfounded opinion or idea. Synonyms: hallucination. Examples: "He has delusions of competence." "His dreams of vast wealth are a hallucination."

(noun) the act of deluding; deception by creating illusory ideas. Synonyms: illusion, head game.