mid-14c., "act of deception," from Old French illusion "a mocking, deceit, deception" (12c.), from Latin illusionem (nominative illusio) "a mocking, jesting, irony," from illudere "mock at," literally "to play with," from assimilated form of in- "at, upon" (see in- (2)) + ludere "to play" (see ludicrous). Sense of "deceptive appearance" developed in Church Latin and was attested in English by late 14c. Related: Illusioned "full of illusions" (1920).
illusion il·lu·sion (ĭ-lōō'zhən)
An erroneous perception of reality.
An erroneous concept or belief.
The condition of being deceived by a false perception or belief.
Something, such as a fantastic plan or desire, that causes an erroneous belief or perception.