A lunatic in an asylum, engraving of 1828.

Lunatic is an old term that was used to refer to a person with a mental illness, or a mental disability. The term goes back to the Latin word lunaticus, which means ' of the moon', or moonstruck. It was also used in English law until about 1930, when it was replaced by "person of unsound mind". Starting 1959, English law speaks about "mental illness".