delusion

noun

de·​lu·​sion di-ˈlü-zhən 

dē-

1

a

: something that is falsely or delusively believed or propagated

under the delusion that they will finish on schedule

delusions of grandeur

b

psychology : a persistent false psychotic belief regarding the self or persons or objects outside the self that is maintained despite indisputable evidence to the contrary

the delusion that someone was out to hurt him

also : the abnormal state marked by such beliefs

2

: the act of tricking or deceiving someone : the state of being deluded

… accused the Bohemian of having practised the most abominable arts of delusion among the younger brethren.

—Walter Scott

delusional

di-ˈlüzh-nəl 

dē-

-ˈlü-zhə-nᵊl

adjective

delusionary

di-ˈlü-zhə-ˌner-ē 

dē-

adjective

Synonyms

• illusion
• dream
• fantasy
• daydream
• vision

Choose the Right Synonym for delusion

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 delusion in a Sentence

He has delusions about how much money he can make at that job.

He is living under the delusion that he is incapable of making mistakes.

She is under the delusion that we will finish on time.

As the illness progressed, his delusions took over and he had violent outbursts.

Recent Examples on the Web

The private and personalized nature of AI use makes its mental health impact difficult to track, but the evidence of potential harms is mounting, from professional apathy to attachments to new forms of delusion. —Parmy Olson, Mercury News, 12 July 2025

At his trial, Fish's children described a chaotic home life marked by erratic behavior, religious delusions and violence. —Christina Coulter, People.com, 12 July 2025

The Leaders Who Listen Win In The Long Run Cultures that survive and thrive are those that invite disagreement, reward constructive tension and embrace data over delusion. —Oscar Chavez-Arrieta, Forbes.com, 20 June 2025

Researchers noted the positive effects of ecstatic epilepsy and synthesized fifty-three theoretical models of delusion. —Rafil Kroll-Zaidi, Harpers Magazine, 21 June 2025

Word History

Etymology

Middle English dilusioun "deceit," borrowed from Late Latin dēlūsiōn-, dēlūsiō "trickery, deceiving," from Latin dēlūdere "to deceive, dupe" + -tiōn-, -tiō, suffix of verbal action — more at delude

First Known Use

15th century, in the meaning defined at sense 2

Phrases Containing delusion

• labor under a delusion/misapprehension/misconception
• self-delusion

Rhymes for delusion

• allusion
• collusion
• conclusion
• confusion
• contusion
• diffusion
• effusion
• exclusion
• extrusion
• illusion
• inclusion
• infusion

Kids Definition

delusion

noun

de·​lu·​sion di-ˈlü-zhən 

1

: the act of deluding : the state of being deluded

2

a

: a mistaken or misleading belief

b

: a false belief that persists despite evidence proving it false and occurs especially in some mentally disturbed states

delusional

-ˈlüzh-nəl 

-ən-ᵊl

adjective

Medical Definition

delusion

noun

de·​lu·​sion di-ˈlü-zhən 

1

a

: the act of deluding : the state of being deluded

b

: an abnormal mental state characterized by the occurrence of psychotic delusions

2

: a false belief regarding the self or persons or objects outside the self that persists despite the facts and occurs in some psychotic states compare hallucination sense 1, illusion sense 2a