How did "lunatic" evolve to mean "crazy"?
I know what the word "lunatic" means and it has something to do with the "Moon" as the "Online Etymology Dictionary" explains:
late 13c., "affected with periodic insanity, dependent on the changes of the moon," from Old French lunatique, lunage "insane," or directly from Late Latin lunaticus "moon-struck," from Latin luna "moon" (see Luna). Compare Old English monseoc "lunatic," literally "moon-sick;" Middle High German lune "humor, temper, mood, whim, fancy" (German Laune), from Latin luna. Compare also New Testament Greek seleniazomai "be epileptic," from selene "moon." Lunatic fringe (1913) apparently was coined by U.S. politician Theodore Roosevelt.
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"Lunar" and "Lunatic" seem to have evolved in a different way. Was there any etymological reason why they had to use "lunatic" in place of "lunar" for "crazy"? How did "lunatic" evolve to mean "crazy"? (I could guess, but I don't exactly understand what "moon-struck" and "moon-sick" mean in the the above.)
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Does suffix "-tic" have any special function itself or was it just used to make a different adjective from "lunar" because the Moon was called "luna" in Latin? I found a list of words that ends with "-tic", but I can't find anything in common.
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If someone was called crazy just because he was affected by the Moon's cycle, is there a word that has anything to do with the Sun's cycle meaning "a bit less crazy" or "more mentally stable than lunatic", etc?
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Why does "lunatic" have a stronger connotation than crazy, insane, out of mind, etc.?
Edit: @Elian commented, "In France, lunatique means something along the lines of erratic or mercurial."
Solution 1:
It was believed that epilepsy seizures were triggered by moonlight hence lunatic was used for those patients.
Luna gives the adjective lunaticus. This appears in the Vulgate (405) of the Dalmatian Christian writer Saint Jerome (Eusebius Hieronymus, 348–420) as an epithet for “a moon-struck” person, whence “crazed, insane, lunatic.” It was used of epilepsy, from the notion that the seizures were precipitated by moonlight. The paroxysmal nature of the disease was thought to be dependent upon the phases of the moon.
Lexicon Orthopaedic Etymology
There is also a scientific publication titled The disease of the moon: the linguistic and pathological evolution of the English term "lunatic" from ncbi.nlm.nih.gov that the origin of the word is related to epilepsy:
The original meaning of the term “lunaticus” is not related only to insanity. In particular, its first use is documented in the Vulgate, the fifth-century Latin version of the Bible,translated from the Ancient Greek by Jerome (347–420) on commission of Pope Damasus.
In the Gospel of Matthew (17: 15–18), a father asks Jesus to cure his son because he is “lunaticus” (“Domine, misere filio meo, quia lunaticus est, et male patitur: nam saepecadit in ignem et crebro in aquam. [ . . . ] Et increpavit illum Jesus et exit ab eo daemo-nium et curatus est puer ex illa hora”). This episode is translated in the Bible of King James (1611) as follows: “Lord, have mercy on my son: for he is lunatick, and sore vexed; for ofttimes he falleth into the fire, and oft into the water [ . . . ] And Jesus rebuked the devil; and he departed out of him: and the child was cured from that very hour.” When this passage is compared with the other synoptic gospels (Luke 9: 37–43; Mark 9: 17–29), the most accurate description of the same episode leads us to understand that the boy is affected by epilepsy.
The term “lunaticus est” is the Latin translation of the Greek verb “ σεληνιαζεται ” (“seleniazetai”), which includes the prefix selen- (from σεληνη - the ancient Greek word for the moon). Therefore, the original meaning of the term “lunatic” seems to be linked to epilepsy, rather than insanity.
You can read about the legal category of lunacy and the history of the word in psychiatry in the book The Moon and Madness (By Niall McCrae).
Solution 2:
Just to comment, in Russian we have "lunatic" word as something between the moon and crazy -- in Russian "lunatic" means a person who walks at night while still sleeping.
And also Oxford dictionary says about this word: "Originally from the Latin lunaticus (luna = moon), because people believed that the changes in the moon made people go mad temporarily."
http://www.oxfordlearnersdictionaries.com/definition/english/lunatic_1?q=lunatic