hallucination

noun

hal·​lu·​ci·​na·​tion hə-ˌlü-sə-ˈnā-shən 

plural hallucinations

1

a

: a sensory perception (such as a visual image or a sound) that occurs in the absence of an actual external stimulus and usually arises from neurological disturbance (such as that associated with delirium tremens, schizophrenia, Parkinson's disease, or narcolepsy) or in response to drugs (such as LSD or phencyclidine)

visual/auditory/olfactory/gustatory/tactile hallucinations

a drug-induced hallucination

An important aspect of the study of hallucinations is the judgement of reality. How does a patient confer the character of reality on stimuli which, beyond any reasonable doubt, originate in his own mind?

—Cesare Davalli et al.

b

: the object of a hallucinatory perception

wasn't sure if the creature was real or a hallucination

2

: an unfounded or mistaken impression or notion : delusion

… that popular hallucination, from which not even great scientists are … free …

—Lewis Mumford

3

computing : a plausible but false or misleading response generated by an artificial intelligence algorithm

"This type of artificial intelligence we're talking about can sometimes lead to something we call hallucination," said Prabhakar Raghavan in an interview with Germany's Welt am Sonntag newspaper published on Saturday. "This is then expressed in such a way that a machine delivers a convincing but completely fictitious answer."

—Matthew Broersma

Synonyms

• illusion
• dream
• daydream
• fantasy
• vision
• delusion

Choose the Right Synonym for hallucination

delusion, illusion, hallucination, mirage mean something that is believed to be true or real but that is actually false or unreal.

delusion implies an inability to distinguish between what is real and what only seems to be real, often as the result of a disordered state of mind.

delusions of persecution

illusion implies a false ascribing of reality based on what one sees or imagines.

an illusion of safety

hallucination implies impressions that are the product of disordered senses, as because of mental illness or drugs.

suffered from terrifying hallucinations

mirage in its extended sense applies to an illusory vision, dream, hope, or aim.

claimed a balanced budget is a mirage

Examples of hallucination in a Sentence

He could not tell if what he was seeing was real or if it was a hallucination.

He has been having hallucinations due to the medication.

Recent Examples on the Web

Ruiz’s father told San Antonio Express-News that his son had been exhibiting signs of a mental disorder, including having hallucinations and making paranoid accusations, in the days leading up to the stabbing. —David Matthews, New York Daily News, 2 July 2025

On Thursday, June 26, the father of 14-year-old Zane Wach shared an update on the teen's health following an incident two weeks ago, in which Zane began experiencing hallucinations due to what doctors believe was altitude sickness. —Charlotte Phillipp, People.com, 29 June 2025

Serious side effects are rare but need quick medical attention, including chest pain, hallucinations, or suicidal thoughts. —Sarah Jividen, Verywell Health, 26 June 2025

But in other cases, the model simply tried to cheat again—removing the markers the researchers used to detect hallucinations, even when the prompt the researchers used told the model explicitly not to do this. —Jeremy Kahn, Fortune, 19 June 2025

Word History

Etymology

see hallucinate

First Known Use

1629, in the meaning defined at sense 1a

Rhymes for hallucination

• abbreviation
• abomination
• acceleration
• accentuation
• accommodation
• accreditation
• acculturation
• accumulation
• acetylation
• adjudication
• administration
• adulteration

Kids Definition

hallucination

noun

hal·​lu·​ci·​na·​tion hə-ˌlüs-ə-ˈnā-shən 

: the awareness of something (as a visual image, a sound, or a smell) that seems to be experienced through one of the senses but is not real, cannot be sensed by someone else, and is usually the result of mental illness or the effect of a drug

also : something of which one is aware but which is not real

Medical Definition

hallucination

noun

hal·​lu·​ci·​na·​tion hə-ˌlüs-ᵊn-ˈā-shən 

1

: a sensory perception (as a visual image or a sound) that occurs in the absence of an actual external stimulus and usually arises from neurological disturbance (as that associated with delirium tremens, Lewy body disease, schizophrenia, Parkinson's disease, or narcolepsy) or in response to drugs (as LSD or phencyclidine)

visual/auditory/olfactory/gustatory/tactile hallucinations

a drug-induced hallucination

compare delusion sense 2, illusion sense 2a

2

: the object of a hallucinatory perception