Definition of "optical illusion" []

• A visually perceived image that is deceptive or misleading. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "“second inequality,” i.e. the optical illusion caused by the earth's annual motion, but first revived an old idea of his own that for the sake of uniformity the sun, or as he preferred to regard it, the earth, should have an equant as well as the planets."
• "Anyone less motivated would not have found the ancient fumarole, its volcanic vapors long since spent, for it lay behind a seemingly uninterrupted wall of basalt formed in tall columnar crystals; nose down, Publius Vagiennius sniffed his way around an optical illusion and found a huge chimney."