Source : Webster's Revised Unabridged Dictionary (1913)

Hallucination \Hal*lu`ci*na"tion\, n. [L. hallucinatio: cf. F.
   hallucination.]
   1. The act of hallucinating; a wandering of the mind; error;
      mistake; a blunder.

            This must have been the hallucination of the
            transcriber.                          --Addison.

Source : WordNet®

hallucination
     n 1: illusory perception; a common symptom of severe mental
          disorder
     2: a mistaken or unfounded opinion or idea; "he has delusions
        of competence"; "his dreams of vast wealth are a
        hallucination" [syn: {delusion}]
     3: an object perceived during a hallucinatory episode; "he
        refused to believe that the angel was a hallucination"