delusion

Etymology

From Latin delusio.

noun

1. A false belief that is resistant to confrontation with actual facts.
2. The state of being deluded or misled, or process of deluding somebody.
   It is far better to grasp the universe as it really is than to persist in delusion, however satisfying and reassuring.
3. That which is falsely or delusively believed or propagated; false belief; error in belief.
   Hess, always a muddled man though not so doltish as Rosenberg, flew on his own to Britain under the delusion that he could arrange a peace settlement. 1960, William L. Shirer, The Rise and Fall of the Third Reich: A History of Nazi Germany, New York: Simon & Schuster, LCCN 81101072, page 835
4. A fixed, false belief, that will not change, despite evidence to the contrary.