illusion

n.

1. Unreal appearance

   fancy, hallucination, mirage, apparition, ghost, chimera, delusion, deception, fantasy, figment of the imagination, dream, vision, phantasm, image, trick of vision, optical illusion, myth, make-believe, déjà vu (French), paramnesia, castle in Spain, will-o'-the-wisp, ignis fatuus (Latin); see also dream 1, fantasy 2, vision 3, 4.

2. Misconception

   delusion, confusion, false impression; see mistake 2, misunderstanding 1.

illusion suggests the false perception or interpretation of something that has objective existence perspective in drawing gives the illusion of depth; delusion implies belief in something that is contrary to fact or reality, resulting from deception, a misconception, or a mental disorder to have delusions of grandeur; hallucination implies the apparent perception, in nervous or mental disorder, of something external that is actually not present; mirage refers to an optical illusion caused by atmospheric conditions, and, in figurative use, implies an unrealizable hope or aspiration