Hallucination

The act of hallucinating; a wandering of the mind; error; mistake; a blunder.

The perception of objects which have no reality, or of sensations which have no corresponding external cause, arising from disorder or the nervous system, as in delirium tremens; delusion.

an object perceived during a hallucinatory episode; "he refused to believe that the angel was a hallucination"

a mistaken or unfounded opinion or idea; "he has delusions of competence"; "his dreams of vast wealth are a hallucination"

illusory perception; a common symptom of severe mental disorder