1. (Science: psychology) An unreal image presented to the bodily or mental vision; a deceptive appearance; a false show; mockery; hallucination. To cheat the eye with blear illusions. (Milton)
2. Hence: Anything agreeably fascinating and charning; enchantment; witchery; glamour. Ye soft illusions, dear deceits, arise! (Pope)
3. (Science: physiology) a sensation originated by some external object, but so modified as in any way to lead to an erroneous perception; as when the rolling of a wagon is mistaken for thunder.
Some modern writers distinguish between an illusion and hallucination, regarding the former as originating with some external object, and the latter as having no objective occasion whatever. Illusion refers particularly to errors of the sense, delusion to false hopes or deceptions of the mind. An optical deception is an illusion, a false opinion is a delusion.
Synonym: delusion, mockery, deception, chimera, fallacy.
Origin: f. Illusion, L. Illusio, fr. Illudere, illusum, to illude.