delusion
Definitions
A persistent false belief held despite strong evidence to the contrary.
The act of deceiving or the state of being deceived.
A belief that is not in accord with reality, often associated with a mental disorder.
Examples
He was under the delusion that he could finish the entire project in a single afternoon.
The politician's belief that he would win by a landslide was nothing more than a dangerous delusion.
Synonyms
illusion hallucination fantasy misconception fallacy mirage deception