delusional
Americanadjective
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having false or unrealistic beliefs or opinions.
Senators who think they will get agreement on a comprehensive tax bill are delusional.
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Psychiatry. maintaining fixed false beliefs even when confronted with facts, usually as a result of mental illness.
He was so delusional and paranoid that he thought everybody was conspiring against him.
Etymology
Origin of delusional
First recorded in 1850–60; delusion ( def. ) + -al 1 ( def. )
Explanation
A delusional person believes things that couldn't possibly be true. If you're convinced that the microwave is attempting to control your thoughts, you are, sadly, delusional. Delusional comes from a Latin word meaning "deceiving." So delusional thinking is kind of like deceiving yourself by believing outrageous things. Delusional thoughts are often a sign of mental illness, but the word can also be used more loosely to describe behavior that is just not realistic. If your friend thinks he's going to get rich playing video games, he's probably not mentally ill, but it's not a stretch to call him delusional.
Vocabulary lists containing delusional
Amari and the Night Brothers
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Far from the Tree
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Schooled
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
Plus, how chatbots can amplify delusional thinking, inside Sam Altman’s personal investments and inflationary risk from data centers.
From The Wall Street Journal • Jun. 28, 2026
Between the six of you, you’re touching on some powerful and risky themes in the series that you’re working on, whether it’s sexism, classism, delusional power, grief.
From Los Angeles Times • Jun. 16, 2026
Osler says this makes chatbots capable of reinforcing delusional thinking.
From The Wall Street Journal • May 25, 2026
Lucy Osler of the University of Exeter examined how interactions with conversational AI could contribute to false beliefs, distorted memories, altered personal narratives, and even delusional thinking.
From Science Daily • May 11, 2026
Most people would have written me off as a delusional lunatic, but Diego treated me like he believed what I was saying, or at least believed that I believed it.
From "We Are the Ants" by Shaun David Hutchinson
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
