il·lu·sion 
(ĭ-lzhən)
(ĭ-lzhən)n.
1.
a. An erroneous perception of reality: Mirrors gave the illusion of spaciousness.
b. An erroneous concept or belief: The notion that money can buy happiness is an illusion.
2. The condition of being deceived by a false perception or belief: spent months flailing about in illusion.
3. Something that is erroneously perceived or construed: The animal in the shadows turned out to be an illusion.
4. A fine transparent net fabric, used for dresses or trimmings.
[Middle English illusioun, from Old French, from Late Latin illūsiō, illūsiōn-, from Latin, a mocking, irony, from illūsus, past participle of illūdere, to mock : in-, against; see IN-2 + lūdere, to play; see leid- in the Appendix of Indo-European roots.]
il·lusion·al, il·lusion·ar′y (-zhə-nĕr′ē) adj.
il·lusion·less adj.
illusiontop: straight horizontal rules appear curved
bottom: a gray box against a black background appears lighter than the same gray box against a white background