illusion Definition

illusion
noun

1. A deceptive or misleading appearance.

Example: A mirage is an optical illusion
Thesaurus: hallucination, apparition, delusion, deception, image, figment of the imagination, ghost, chimera.
2. A false or misleading impression, idea, belief or understanding.

Example: was under the illusion he worked here
Thesaurus: misconception, false impression, confusion.
3. psychol.
A false perception of an object or experience due to the mind misinterpreting the evidence relayed to it by the senses. Compare delusion, hallucination.

Etymology: 14c: from Latin illusio irony, mocking or deceit, from illudere to mock or make fun of someone.