hallucination

American  

[huh-loo-suh-ney-shuhn] / həˌlu səˈneɪ ʃən /

noun

1. 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 usually manifested as visual or auditory images.

   Synonyms:

   aberration, phantasm

2. the sensation caused by a hallucinatory condition, or the object or scene visualized.

3. a false notion, belief, or impression; illusion; delusion.

4. Computers, Digital Technology. (in the field of machine learning) false information generated by a machine learning program contrary to the intent of the user and presented as if it were true and factual.

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hallucination British  

/ həˌluːsɪˈneɪʃən /

noun

1. the alleged perception of an object when no object is present, occurring under hypnosis, in some mental disorders, etc

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hallucination Cultural  

1. A false perception that appears to be real, as when, for example, a man dying of thirst in a desert thinks that he sees a lake. (See also delusion.)

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Usage

What is a hallucination? A hallucination is a sensory experience of something that does not actually exist and has no basis in reality. Hallucinations can be caused by mental disorders or toxic substances. A hallucination often takes the form of visual images or noises, as in Sangeet saw a hallucination of sparkling lights. Hallucination can also be used to refer to the sensation caused by one of these false sensory experiences, as in Roman was suffering from drug-induced hallucinations. More generally, hallucination can be used to mean a false notion or belief, as in His idea of what life was like in Canada was nothing more than a silly hallucination. Hallucination is similar to the words illusion and delusion, which also describe false beliefs or experiences. An illusion is a false image that is a result of a distortion or manipulation of actual things. For example, makeup can create the illusion that a person is younger than they actually are. A delusion is a persistent, false belief that may or may not be partially based on reality, as in The athlete’s huge ego constantly made him have delusions of being unbeatable. Example: The explorer suffered from terrifying hallucinations of ghosts and phantoms after eating the toxic mushrooms.

Related Words

See illusion.

Other Word Forms

• hallucinational adjective
• hallucinative adjective
• nonhallucination noun

Etymology

Origin of hallucination

First recorded in 1640–50; from Latin hallūcinātiōn-, stem of hallūcinātiō, variant of (h)ālūcinātiō, “a wandering of the mind”; hallucinate + -ion

Explanation

If you see your teacher morph into a dancing elephant, chances are you’re having a hallucination, or an illusory perception. In other words, it sounds like you are seeing things! A person experiencing a hallucination perceives things that aren’t really there. A hallucination can involve any of the senses — including sight, hearing, touch, smell, and taste — and often results from a mental disorder or a chemical source, such as a drug.

Example Sentences

"We're in a state of hallucination," says Éva Bognár, a researcher at the Central European University's Democracy Institute.

From BBC • Apr. 4, 2026

Founder Shield incorporates "AI malfunction and hallucination" scenarios specifically into professional services policies covering losses the technology causes clients.

From Barron's • Mar. 15, 2026

These included conditions such as seizures, altered mental status, and hallucination.

From Science Daily • Jan. 5, 2026

This AI hallucination problem remains a significant obstacle to fully autonomous cyberattacks—at least for now.

From The Wall Street Journal • Nov. 23, 2025

My befuddled brain simply thinks it’s another hallucination and I wait for it to disappear.

From "Woodsong" by Gary Paulsen

Related Words

• illusion
• phantom