1.NounA distortion of sensory perception where real stimuli lead to a false or misleading impression of reality.
"We saw what looked like a tiger among the trees, but it was an illusion caused by the shadows of the branches.; Using artificial additives, scientists can create the illusion of fruit flavours in food."
2.NounA misapprehension; a belief in something that is in fact not true.
"Jane has this illusion that John is in love with her."