hal·​lu·​ci·​na·​tion hə-ˌlü-sə-ˈnā-shən How to pronounce hallucination (audio)
plural hallucinations
: 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.
: the object of a hallucinatory perception
wasn't sure if the creature was real or a hallucination
: an unfounded or mistaken impression or notion : delusion
… that popular hallucination, from which not even great scientists are … free … — Lewis Mumford
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
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 Others showed up at hospitals with a variety of other serious symptoms, including hallucinations and vomiting. Alexander Tin, CBS News, 22 Nov. 2023 McAfee did indicate that one of the biggest risks related to generative AI is hallucinations—a response that may sound plausible but is factually incorrect or unrelated to the context. Sheryl Estrada, Fortune, 13 Nov. 2023 Combing through the Borneo jungle for answers, each member of Dr. Sani’s team experiences inexplicable hallucinations, malicious disturbances and eventually are haunted by unexplained spirits of the dead. Patrick Frater, Variety, 26 Oct. 2023 Akunyili Crosby employs this method to create careful hallucinations, layering memories over moments that otherwise live fully in the now. The Beautiful Ones, Vulture, 24 Oct. 2023 These symptoms are more advanced than those of normal aging—such as forgetting which words to use and occasionally losing things—but less severe than those of Alzheimer’s—such as getting lost in places that should be familiar, or having hallucinations. Maggie O'Neill, Health, 2 Nov. 2023 Such behaviors include: Hitting Slapping Shoving Grabbing Pinching Biting Hair pulling More seriously, extremes of both hypoglycemia or hyperglycemia can lead to cognitive impairment, confusion, loss of self-control, or hallucinations. Debra Manzella, Verywell Health, 21 Oct. 2023 Long before the killing, Murphy had a history of severe mental illness, including visual hallucinations and dissociative blackouts. Keri Blakinger, Los Angeles Times, 11 Oct. 2023 But there’s been plenty of room for errors and hallucinations, instances when chatbots like ChatGPT have concocted inaccurate—and sometimes worrying—answers to questions. Joseph Abrams, Fortune, 6 Oct. 2023 See More

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'hallucination.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


see hallucinate

First Known Use

1629, in the meaning defined at sense 1a

Time Traveler
The first known use of hallucination was in 1629

Dictionary Entries Near hallucination

Cite this Entry

“Hallucination.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/hallucination. Accessed 3 Dec. 2023.

Kids Definition


hal·​lu·​ci·​na·​tion hə-ˌlüs-ə-ˈnā-shən How to pronounce hallucination (audio)
: 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 disorder or the effect of a drug
also : something of which one is aware but which is not real

Medical Definition


hal·​lu·​ci·​na·​tion hə-ˌlüs-ᵊn-ˈā-shən How to pronounce hallucination (audio)
: 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
: the object of a hallucinatory perception
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