illusion (n.)

mid-14c., "mockery, scorning, derision;" late 14c., "act of deception; deceptive appearance, apparition; delusion of the mind," from Old French illusion "a mocking, deceit, deception" (12c.), from Latin illusionem (nominative illusio) "a mocking, jesting, jeering; irony," from past-participle stem of illudere "mock at," literally "to play with," from assimilated form of in- "at, upon" (from PIE root *en "in") + ludere "to play" (see ludicrous). Sense of "deceptive appearance" first developed in Church Latin. Related: Illusioned "full of illusions" (1920).