- a false idea or conception; belief or opinion not in accord with the facts
- an unreal, deceptive, or misleading appearance or image: a large mirror giving the illusion of space in a small room
- a trick, as one designed or performed by a stage magician, appearing to defy ordinary physical laws
- a false perception, conception, or interpretation of what one sees, where one is, etc.
- the misleading image resulting in such a false impression
- a delicate, gauzy silk tulle used for veils, etc.
Origin of illusionMiddle English illusioun from Old French illusion from Classical Latin illusio, a mocking (in LL(Ec), deceit, illusion) from illusus, past participle of illudere, to mock, play with from in-, on + ludere, to play: see ludicrous