noun (n)

• an erroneous mental representation(noun.cognition)

  Synonym:
  semblance
  

  source: wordnet30
• something many people believe that is false(noun.cognition)

  Example:
  They have the illusion that I am very wealthy.
  

  Synonym:
  fancy, fantasy, phantasy
  

  source: wordnet30
• the act of deluding; deception by creating illusory ideas(noun.act)

  Synonym:
  delusion, head game
  

  source: wordnet30
• an illusory feat; considered magical by naive observers(noun.act)

  Synonym:
  conjuration, conjuring trick, deception, legerdemain, magic, magic trick, thaumaturgy, trick
  

  source: wordnet30
• An unreal image presented to the bodily or mental vision; a deceptive appearance; a false show; mockery; hallucination.(noun)

  source: webster1913