WordNet sense 1 (an erroneous mental representation):

semblance

WordNet sense 2 (something many people believe that is false):

fancy, fantasy, phantasy

WordNet sense 3 (the act of deluding; deception by creating illusory ideas):

delusion, head game

WordNet sense 4 (an illusory feat; considered magical by naive observers):

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