Lunatic

n. crazy or deranged person, insane person; person who is reckless or extremely foolish

adj. crazy, insane; not mentally sound; of or for the insane; foolish, extremely reckless

A lunatic (colloquially: "looney") is a commonly used term for a person who is mentally ill, dangerous, foolish or unpredictable, a condition once called lunacy.The word lunatic is borrowed from Latin "lunaticus", which gains its stem from "luna" for moon, which denotes the traditional link made in folklore between madness and the phases of the moon. This probably refers to the symptoms of cyclic mood disorders such as bipolar disorder or cyclothymia, the symptoms of which may also go through phases. As yet there is little evidence for any causal link between phases of the moon and the progression of mood disorder symptoms.
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Noun
1. an insane person
(synonym) madman, maniac
(hypernym) sick person, diseased person, sufferer
(hyponym) crazy, loony, looney, weirdo
2. a reckless impetuous irresponsible person
(synonym) daredevil, madcap, hothead, swashbuckler, harum-scarum
(hypernym) adventurer, venturer
(hyponym) tearaway
Adjective
1. insane and believed to be affected by the phases of the moon
(synonym) moonstruck
(similar) insane
(classification) colloquialism

(n.)
A person affected by lunacy; an insane person, esp. one who has lucid intervals; a madman; a person of unsound mind.
  

(a.)
Of or pertaining to, or suitable for, an insane person; evincing lunacy; as, lunatic gibberish; a lunatic asylum.
  

(a.)
Affected by lunacy; insane; mad.
  

An individual of unsound mind. - (read more on Lunatic)