Definitions for hallucinationhəˌlu səˈneɪ ʃən

Random House Webster's College Dictionary

hal•lu•ci•na•tionhəˌlu səˈneɪ ʃən(n.)

a sensory experience of something that does not exist outside the mind, caused by various physical and mental disorders, or by reaction to certain toxic substances, and usu. manifested as visual or auditory images.
Category: Psychiatry
the sensation caused by a hallucinatory condition or the object or scene visualized.
Category: Psychiatry
a false belief or impression; illusion; delusion.

Origin of hallucination:

1640–50; < L

hal•lu`ci•na′tion•al-ˌneɪ tɪv, -nə tɪv(adj.)

hal•lu′ci•na`tive-ˌneɪ tɪv, -nə tɪv(adj.)

Princeton's WordNet

hallucination(noun)
illusory perception; a common symptom of severe mental disorder
delusion, hallucination(noun)
a mistaken or unfounded opinion or idea
"he has delusions of competence"; "his dreams of vast wealth are a hallucination"
hallucination(noun)
an object perceived during a hallucinatory episode
"he refused to believe that the angel was a hallucination"

Wiktionary

hallucination(Noun)
A sensory perception of something that does not exist, arising from disorder of the nervous system, as in delirium tremens; a delusion.
hallucination(Noun)
The act of hallucinating; a wandering of the mind; an error, mistake or blunder.

Origin: Derives from verb to hallucinate, from hallucinatus. Compare French hallucination. The first known usage in the English language is from Sir Thomas Browne.

Webster Dictionary

Hallucination(noun)
the act of hallucinating; a wandering of the mind; error; mistake; a blunder
Hallucination(noun)
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