ILLUSION

[noun] [C] - an idea or belief which is not true or not what it seems to beWe have no illusions about (= understand and accept) how difficult the job will be.The committee have managed to create the illusion of activity, but they have actually achieved very little.The calm on the streets is an illusion - people are very angry.The magician tricks the audience with skilful optical illusions, making things appear and disappear.The boss is (labouring) under the illusion that (= wrongly believes that) the project will be completed on time.