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.
The paper examined real-world examples in which generative AI systems became part of the cognitive process of individuals who had been clinically diagnosed with hallucinations and delusional thinking.
From Science Daily • May 11, 2026
Which is not to say Yee is delusional.
From Los Angeles Times • Mar. 8, 2026
Numerous studies have found that in its eagerness to agree with the user, the model validated unhealthy or dangerous behaviour, and even led people to delusional thinking.
From BBC • Feb. 13, 2026
By August, as problems with users suffering from delusional psychosis appeared in media reports, OpenAI attempted to retire 4o entirely and replace it with a new version, named GPT-5.
From The Wall Street Journal • Feb. 10, 2026
Maybe I shouldn’t have listened to Boggs, because he might have been in some delusional death state.
From "Mockingjay" by Suzanne Collins
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.
