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
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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.
In the test, the latest version of ChatGPT, model 5.2, and Claude were more likely to lead the user away from delusional thinking.
From BBC • May 2, 2026
Even so, there is a curious — and hopefully not delusional — optimism in classical music, L.A. style.
From Los Angeles Times • Apr. 3, 2026
While the “number of users” once meant “number of paying users,” the success of Facebook, Instagram and other social-media sites persuaded delusional investors that the word “paying” could be dropped.
From MarketWatch • Feb. 6, 2026
Girgis and his peers have tested ChatGPT and Claude for how they handle delusional or paranoid thoughts.
From Slate • Feb. 2, 2026
The accurate thing to say is that it is delusional.
From "The Mona Lisa Vanishes" by Nicholas Day
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.
