Black's Law Dictionary (2nd edition)dictionaries

Illusion

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

Source: Black’s Law Dictionary 2nd Ed (1910)