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a. The act or process of deluding.
b. The state of being deluded.
a. A false belief or opinion: labored under the delusion that success was at hand.
b. Psychiatry A false belief or perception that is a manifestation of a mental illness: delusions of persecution.
[Middle English delusioun, from Latin dēlūsiō, dēlūsiōn-, from dēlūsus, past participle of dēlūdere, to delude; see delude.]