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.

  1. "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.)

  2. 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.

  3. 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?

  4. 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."

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    While it doesn't address all parts of the question this from the Daily Beast 6/20/14 is helpful I think "The Queen’s University researchers, led by Varinder Parmar, wrote that the belief in lunar impact might be “a cultural artifact, left over from the time before artificial lighting.” “The full moon provided an increase in the amount of nighttime illumination and caused a significant sleep disturbance as a result,” wrote Parmar et al in their study. “Recent research has shown that sleep disruptions of as little as 1.5 hours from baseline can induce mania and seizures in vulnerable people.”
    – Misneac
    Commented Nov 13, 2015 at 15:28
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    How offensive is the word 'lunatic'? bbc.com/news/magazine-17997413
    – user66974
    Commented Nov 13, 2015 at 15:36
  • What makes you think that it has a stronger connotation? Commented Nov 13, 2015 at 16:38
  • @Rathony In France, "lunatique" means something along the lines of "erratic" or "mercurial."
    – Elian
    Commented Nov 13, 2015 at 16:42
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    I think that a mutable, mercurial nature has always been associated with craziness. Consider the phrase "mentally unstable". Something that's mercurial and changeable, like the moon, is regarded as unstable. I would posit that if you're a lunatic you would partake of the moon's nature and be at least somewhat mentally unbalanced
    – Misneac
    Commented Nov 13, 2015 at 18:46

5 Answers 5


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).


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."


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    "a person who walks at night while still sleeping" Known as a "sleep-walker" in English. Commented Nov 13, 2015 at 22:52
  1. Well, the two terms simply denote different meanings. The same word stem doesn't lead to correlation with other terms in which it's used... (cf. astronomy-astrology)
    As for 'moon-struck', etc., this might help: http://www.scientificamerican.com/article/lunacy-and-the-full-moon/

  2. The suffix "-tic" is Greek, -tikon, and forms adjectives.

    -tikon/-tic = 'pertaining to'. lunatic = 'pertaining to the moon'.

    In the case of lunar, the suffix is simply Latin, but has the same role.

    So no, no special function as such.

  3. If so, then I've never encountered it. Would be interesting, though...

  4. Not to my knowledge, although someone else might think differently.


Just do a corpus search for *tic and *ar and you will see that the former is used for nouns related to personhood (fanatic, romantic) and the latter for adjectives (sometimes related to nominal concepts - familiar, solar, particular).

So 'lunatic' and 'lunar' could easily be derived naturally by analogy even without any direct etymology.

I'm not sure 'lunatic' necessarily has stronger connotations than crazy. But a part of it could be because it describes the person's identity in a total way as opposed just one of its qualities.

  • Thank you for your answer. According to the Etymology Online Dictionary, "lunatic" had been used as an "adjective" first before it became a noun related to a person.
    – user140086
    Commented Nov 14, 2015 at 5:13

Lunatic refers to while on full moon day the gravitational pull ofmoon is higher hence the.salt and water in our body is pulled up n women folks who still mensurate will be effected as they have moon cycle every 28 days mensuration or flow of blood The same pattern in sea also can be found its called high tide n low tide the water raises and again goes back to normal. This is no mental ill or insane or going mad or to a physiatrist

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