In medical jurisprudence. An image or Impression in the mind, excited by some external object addressing itself to one or more of the senses, bnt which, in-stead of corresponding with the reality, is perverted, distorted, or wholly mistaken, the error being attributable to the imagination of the observer, not to any defect in the or-gans of sense. See Hallucination, and see “Delusion,” under Insanity