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[dih-loo-zhuh n] /dɪˈlu ʒən/
an act or instance of deluding.
the state of being deluded.
a false belief or opinion:
delusions of grandeur.
Psychiatry. a fixed false belief that is resistant to reason or confrontation with actual fact:
a paranoid delusion.
Origin of delusion
late Middle English
1375-1425; late Middle English < Latin dēlūsiōn- (stem of dēlūsiō), equivalent to dēlūs(us) (past participle of dēlūdere; see delude) + -iōn- -ion
Related forms
delusional, delusionary, adjective
predelusion, noun
Can be confused
allusion, delusion, elusion, hallucination, illusion (see synonym study at illusion)
1. deception. See illusion. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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Examples from the Web for delusion
Contemporary Examples
Historical Examples
  • The delusion has now vanished, and made room for sober reason and reflection.

    The Grand Old Man Richard B. Cook
  • You are no delusion—no mirage, but Rima, like no other being on earth.

    Green Mansions W. H. Hudson
  • There was, indeed, a resemblance in their size and persons, which favoured the delusion.

  • I hold Nature for Master in such matters, and the fancy of men for delusion.

    Albert Durer T. Sturge Moore
  • "You appear to be laboring under some sort of delusion," he replied.

    The Mystery of Murray Davenport Robert Neilson Stephens
British Dictionary definitions for delusion


a mistaken or misleading opinion, idea, belief, etc: he has delusions of grandeur
(psychiatry) a belief held in the face of evidence to the contrary, that is resistant to all reason See also illusion, hallucination
the act of deluding or state of being deluded
Derived Forms
delusional, adjective
delusive, adjective
delusively, adverb
delusiveness, noun
delusory (dɪˈluːsərɪ) adjective
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for delusion

"act of misleading someone," early 15c.; as a form of mental derangement, 1550s, from Latin delusionem (nominative delusio) "a deceiving," noun of action from past participle stem of deludere (see delude).

Technically, delusion is a belief that, though false, has been surrendered to and accepted by the whole mind as a truth; illusion is an impression that, though false, is entertained provisionally on the recommendation of the senses or the imagination, but awaits full acceptance and may not influence action. Delusions of grandeur, the exact phrase, is recorded from 1840, though the two words were in close association for some time before that.

Online Etymology Dictionary, © 2010 Douglas Harper
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delusion in Medicine

delusion de·lu·sion (dĭ-lōō'zhən)
A false belief strongly held in spite of invalidating evidence, especially as a symptom of mental illness.

de·lu'sion·al adj.
The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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delusion in Science
A false belief strongly held in spite of invalidating evidence, especially as a symptom of mental illness, as in schizophrenia.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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delusion in Culture

delusion definition

A false belief held despite strong evidence against it; self-deception. Delusions are common in some forms of psychosis. Because of his delusions, the literary character Don Quixote attacks a windmill, thinking it is a giant.

The New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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