Delusion
Delusion , noun
[Latin delusio, from deludere. See Delude.]
1.
The act of deluding; deception; a misleading of the mind. — Pope
2.
The state of being deluded or misled.
3.
That which is falsely or delusively believed or propagated; false belief; error in belief.
And fondly mourned the dear delusion gone.