delusion

noun

• False belief despite evidence to the contrary
• An idiosyncratic belief or impression maintained despite being contradicted by reality or rational argument, typically as a symptom of mental disorder.
• A false belief or idea.
• A false belief or judgment about external reality, held despite incontrovertible evidence to the contrary.
• (Psychiatry) A persistent false belief held in the face of evidence to the contrary, especially as a symptom of mental illness.
• A false belief or judgment about external reality, held despite incontrovertible evidence to the contrary.