Pronunciation: (i-lOO'zhun),[key] —n. 1. something that deceives by producing a false or misleading impression of reality.
2. the state or condition of being deceived; misapprehension.
3. an instance of being deceived.
4. Psychol.a perception, as of visual stimuli (optical illusion), that represents what is perceived in a way different from the way it is in reality.
5. a very thin, delicate tulle of silk or nylon having a cobwebbed appearance, for trimmings, veilings, and the like.
6. Obs.the act of deceiving; deception; delusion.