definition of
illusion

[1] #1 illusion n. [semblance] an erroneous mental representation. wn

[2] #2 illusion n. [fantasy, phantasy, fancy] something many people believe that is false; "they have the illusion that I am very wealthy". wn

[3] #3 illusion n. [delusion, head game] the act of deluding; deception by creating illusory ideas. wn

[4] #4 illusion n. [magic trick, conjuring trick, trick, magic, legerdemain, conjuration, thaumaturgy, deception] an illusory feat; considered magical by naive observers. wn