Lunatic

Lunatic is an informal term referring to a person who is considered mentally ill, dangerous, foolish or unpredictable, conditions once attributed to lunacy. The term may be considered insulting in serious contexts in modern times, but is now more likely to be used in friendly jest. The word derives from lunaticus meaning "of the moon" or "moonstruck". The term was once commonly used in law.

The term "lunatic" derives from the Latin word , which originally referred mainly to epilepsy and , as diseases thought to be caused by the moon. KJV records "lunatick" in Mt 17:15 and Mt 4:24. By the fourth and fifth centuries astrologers were commonly using the term to refer to neurological and psychiatric diseases. Philosophers such as Aristotle and Pliny the Elder argued that the full moon induced insane individuals with bipolar disorder by providing light during nights which would otherwise have been dark, and affecting susceptible individuals through the well-known route of sleep deprivation. Until at least 1700 it was also a common belief that the moon influenced fevers, rheumatism, episodes of epilepsy and other diseases.

In the British jurisdiction of England and Wales the Lunacy Acts 1890–1922 referred to "lunatics", but the Mental Treatment Act 1930 changed the legal term to "person of unsound mind", an expression which was replaced under the Mental Health Act 1959 by "mental illness". "Person of unsound mind" was the term used in 1950 in the English version of the European Convention on Human Rights as one of the types of person who could be deprived of liberty by a judicial process. The 1930 Act also replaced the term "asylum" with "mental hospital". Criminal lunatics became Broadmoor patients in 1948 under the National Health Service (Scotland) Act 1947.

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