A strong belief that is clearly false or unrealistic, especially when a person continues to believe it even when given clear proof that it is wrong.
From Latin *deludere* meaning 'to mock, to deceive', from *de-* ('from, down') and *ludere* ('to play'). The original sense was being 'played with' or tricked, which later shifted inward to being tricked by your own mind.
Delusions show how powerful the mind is: you can be completely convinced of something that clashes with reality. The root meaning of 'being played with' is still there—you’re effectively being tricked, sometimes by your own brain.
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