From WordNet (r) 3.0 (2006) [wn]:
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, hallucination]
3: an object perceived during a hallucinatory episode; "he
refused to believe that the angel was a hallucination"
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Hallucination \Hal*lu`ci*na"tion\ (-n[=a]"sh[u^]n), n. [L.
hallucinatio: cf. F. hallucination.]
1. The act of hallucinating; a wandering of the mind; error;
mistake; a blunder.
[1913 Webster]
This must have been the hallucination of the
transcriber. --Addison.
[1913 Webster]
2. (Med.) The perception of objects which have no reality, or
of sensations which have no corresponding external cause,
arising from disorder of the nervous system, as in
delirium tremens; delusion.
[1913 Webster]
Hallucinations are always evidence of cerebral
derangement and are common phenomena of insanity.
--W. A.
Hammond.
[1913 Webster]