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

1375–1425; late Middle English < Latin dēlūsiōn- (stem of dēlūsiō), equivalent to dēlūs(us) (past participle of dēlūdere; see delude) + -iōn- -ion
Related formsde·lu·sion·al, de·lu·sion·ar·y, adjectivepre·de·lu·sion, noun
Can be confusedallusion delusion elusion hallucination illusion (see synonym study at illusion)

Synonyms for delusion Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for delusion

Contemporary Examples of delusion

Historical Examples of delusion

  • 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, etche has delusions of grandeur
psychiatry a belief held in the face of evidence to the contrary, that is resistant to all reasonSee also illusion, hallucination
the act of deluding or state of being deluded
Derived Formsdelusional, adjectivedelusive, adjectivedelusively, adverbdelusiveness, noundelusory (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

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

delusion in Medicine




A false belief strongly held in spite of invalidating evidence, especially as a symptom of mental illness.
Related formsde•lusion•al adj.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

delusion in Science



A false belief or perception strongly held in spite of invalidating evidence, especially as a symptom of mental illness, as in schizophrenia.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

delusion in Culture


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 Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.