1. something with deceptive appearance: something that deceives the senses or mind, e.g. by appearing to exist when it does not or appearing to be one thing when it is in fact another
2. false idea: a false idea, conception, or belief about somebody or something
3. deceptive power of appearances: the ability of appearances to deceive the mind and senses, or the capacity of the mind and senses to be deceived by appearances
4. psychology mistaken sensory perception: a misinterpretation of an experience of sensory perception, especially a visual one, where the stimuli are objectively present and the mistaken perception is due to physical rather than psychological causes
[14th century. Via French< Latin illusion-< illus-, past participle of illudere "play at" < ludus "play, sport"]
