Lunatic

Part of speech: noun, adjective

Pronunciation: /ˈluːnətɪk/

Definitions

1. A person who behaves in a wildly irrational or mentally unstable manner
2. An individual exhibiting erratic behavior or severe mental disturbance is often labeled as such in historical contexts
3. A person characterized by extreme emotional instability or irrational conduct has sometimes been referred to in this manner

Etymology: The belief that the moon can drive people mad is older than the English language itself, and this word preserves it in its very structure. "Lunatic" traces back to Latin "luna," meaning "moon," through Late Latin "lunaticus," which meant "moonstruck." The idea behind it was that the waxing and waning of the moon brought on fits of madness that came and went with its phases, so a person afflicted this way was literally struck by the moon. The word passed into Middle English as "lunatik" by way of Old French "lunatique," which carried the same sense of periodic, moon-driven insanity. Its meaning was once narrower than today's: it described a condition of intermittent derangement rather than a general label for anyone considered mentally unstable. Over the centuries it broadened into the blunt term it is now, and it has since become offensive in most contexts.

Synonyms: madman, insane, crazy, fool, maniac

Antonyms: sane, rational, logical, level-headed, sensible