What does delusion mean?
A delusion is a false belief or impression that a person holds with conviction, even when confronted with clear evidence to the contrary. The word has two main registers of use. In everyday speech it describes any stubborn self-deception — someone may labour under the delusion that they are indispensable at work, or that a failing relationship will fix itself. In psychiatry it carries a stricter meaning: a fixed false belief, such as believing oneself persecuted or possessing special powers, that is a recognised symptom of conditions like schizophrenia and psychotic depression. Delusions differ from illusions, which are distortions of real sensory experience rather than beliefs. The word derives from the Latin deludere, 'to mock or play falsely', and entered English in the late fourteenth century via Old French and Latin. Its synonyms include illusion, fantasy, and misconception.
nounA false belief or impression that is firmly maintained despite being contradicted by reality or rational argument; in psychiatry, a fixed false belief characteristic of certain mental disorders.
- A fixed false belief maintained despite clear contradictory evidence, especially as a symptom of mental illness (as in clinical usage).
- A false belief or deceptive impression held more generally, often about oneself or one's circumstances.
"He clung to the delusion that he would one day be discovered by a talent scout."
"Her belief that she was being followed everywhere turned out to be a symptom of a serious delusional disorder."
"Millions of investors laboured under the delusion that house prices could never fall."
Both countable ('delusions of grandeur') and uncountable uses occur, but the countable plural is standard when referring to individual false beliefs.
"The patient experienced persecutory delusions throughout the acute phase of his illness."
The Latin root of 'delusion' literally means 'to mock or play games with' — every delusion is, etymologically speaking, a trick someone is playing on you.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of delusion
'Delusion' comes from the Latin verb deludere, formed from de- ('away from' or intensifying) plus ludere ('to play'), so the original sense is 'to play false with', 'to mock', or 'to deceive'. It passed into English via Old French delusion around the late fourteenth century, initially meaning deception or mockery before narrowing toward self-deception and false belief. It shares its root with words such as delude, elude, ludicrous, and illusion (from the related Latin illudere), all built on the same playful-yet-deceptive stem ludere.
Related word forms
How delusion is actually used
In everyday use, 'delusion' often carries a mild, even affectionate connotation of self-deception ('the delusion that she could quit anytime'). In psychiatric and clinical contexts it has a precise technical meaning: a fixed, false belief resistant to reason or contrary proof, and its use implies a significant departure from reality. Because of this clinical weight, describing someone's ordinary mistaken opinion as a 'delusion' can sound dismissive or insulting.
Easily confused with delusion
An illusion is a misperception of a real external stimulus (such as an optical illusion), whereas a delusion is a false belief held with conviction despite evidence against it.