sane (adj.)

"of sound mind, mentally sound," 1721, a back-formation from insane or sanity or else from Latin sanus "sound, healthy," in its figurative or transferred use, "of sound mind, rational, sane," also, of style, "correct;" a word of uncertain origin.

It is perhaps from PIE *seh-no- from *seh- "to tie." That reconstruction "is purely mechanical," according to de Vaan, the meaning might be "which is in place, in order." Or it could be from a different root meaning "to satisfy" as in Latin satis "enough."

Used earlier, of the body, with a sense of "healthy" (1620s), but this has been rare in English. OED writes, "The almost entire restriction in English to a sense 'mentally sound' is due to the use in antithesis with insane, which (like the Latin insanus, its source) always referred to mental condition." Related: Sanely; saneness.

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sanitarium (n.)

1829, "an improper form for sanatorium" [Century Dictionary], meant to indicate "place dedicated to health," perhaps based on sanitary or from Latin sanitas "health," from sanus "healthy; sane" (see sane).

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sanity (n.)

early 15c., sanite, "healthy condition, health," a sense now obsolete, from Old French sanité "health," from Latin sanitatem (nominative sanitas) "health, soundness of body; sanity, soundness of mind; reason; correctness of speech;" from sanus "healthy; sane" (see sane). Meaning "soundness of mind" is attested from c. 1600.

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insane (adj.)
1550s, of persons, "mentally damaged," from Latin insanus "mad, insane, of unsound mind; outrageous, excessive, extravagant," from in- "not" (see in- (1)) + sanus "well, healthy, sane" (see sane). In reference to actions, "irrational, evidencing madness," from 1842 in English. The noun meaning "insane person" is attested from 1786. For the notion of insanity as sickness, compare lunatic; and Italian pazzo "insane," originally a euphemism, from Latin patiens "suffering." German verrückt, literally past participle of verrücken "to displace," "applied to the brain as to a clock that is 'out of order' " [Buck].
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sanitary (adj.)

1823, "pertaining to health or hygiene," from French sanitaire (1812), from Latin sanitas "health," from sanus "healthy; sane" (see sane). In reference to menstrual devices, by 1881 (in sanitary towel). In U.S. history the Sanitary Commission, created by the Secretary of War in 1861, provided relief to soldiers and oversaw military lodging and hospitals. Sanitarian is by 1859 as "promoter of, or one versed in, sanitary measures or reforms;" sanitarist in that sense also is by 1859.

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sanatorium (n.)

by 1839 as "hospital, usually private, for the treatment of invalids, convalescents, etc., who might benefit from open air;" by 1842 as "place to which people go for the sake of health or to regain health;" Modern Latin, noun use of neuter of Late Latin adjective sanitorius "health-giving," from Latin sanat-, past-participle stem of sanare "to heal," from sanus "well, healthy, sane" (see sane).

Latin sanare is the source of Italian sanare, Spanish sanar. Century Dictionary [1895] notes it was "specifically applied to military stations on the mountains or tablelands of tropical countries, with climates suited to the health of Europeans."

Many of his patients had asked him what this hard word sanatorium meant, and he explained to them, that it was a lodging-house, which was, in fact, the proper alias of sanatorium, and that it was to the benefit of Dr. Arnott's stove and of regularity in the time of giving medicine. [from report on a "Debate on the Sanatorium" in The Lancet, Jan. 11, 1840]
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mens sana in corpore sano 

c. 1600, Latin, literally "a sound mind in a sound body," a line found in Juvenal, "Satires," x.356.

Mens sana in corpore sano is a contradiction in terms, the fantasy of a Mr. Have-your-cake-and-eat-it. No sane man can afford to dispense with debilitating pleasures; no ascetic can be considered reliably sane. Hitler was the archetype of the abstemious man. When the other krauts saw him drink water in the Beer Hall they should have known he was not to be trusted. [A.J. Liebling, "Between Meals," 1962]
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Catch-22 (n.)

from the title of Joseph Heller's 1961 novel. In widespread use only after release of the movie based on the book in 1970. The catch (n.) is that a bomber pilot is insane if he flies combat missions without asking to be relieved from duty and thus is eligible to be relieved from duty. But asking to be relieved from duty indicates sanity and thus he must keep flying missions.

There was only one catch and that was Catch-22, which specified that a concern for one's safety in the face of dangers that were real and immediate was the process of a rational mind. Orr was crazy and could be grounded. All he had to do was ask; and as soon as he did, he would no longer be crazy and would have to fly more missions. Orr would be crazy to fly more missions and sane if he didn't, but if he was sane he had to fly them. If he flew them he was crazy and didn't have to; but if he didn't want to he was sane and had to. Yossarian was moved very deeply by the absolute simplicity of this clause of Catch-22 and let out a respectful whistle.

"That's some catch, that Catch-22," he observed.

"It's the best there is," Doc Daneeka agreed.
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salesmanship (n.)

"character or qualities of a (good) salesman," 1853, from salesman + -ship.

The modern system of salesmanship has become so much like persecution reduced to a science, that it is quite a luxury to be allowed the use of your own discretion, without being dragooned, by a shopkeeper's deputy, into looking at what you do not care to see, or buying what you would not have. A man in his sane mind, with the usual organs of speech, has a right to be treated as if he knows what he wants, and is able to ask for it. [The Literary World, Feb. 26, 1853]
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wise (adj.)

Old English wis "learned, sagacious, cunning; sane; prudent, discreet; experienced; having the power of discerning and judging rightly," from Proto-Germanic *wissaz (source also of Old Saxon, Old Frisian wis, Old Norse viss, Dutch wijs, German weise "wise"), from past-participle adjective *wittos of PIE root *weid- "to see" (hence "to know"). Modern slang meaning "aware, cunning" first attested 1896. Related to the source of Old English witan "to know, wit."

A wise man has no extensive knowledge; He who has extensive knowledge is not a wise man. [Lao-tzu, "Tao te Ching," c. 550 B.C.E.]

Wise man was in Old English. Wise guy is attested from 1896, American English; wise-ass (n.) by 1966, American English (probably a literal sense is intended by the phrase in the 1607 comedy "Westward Hoe" by Dekker and Webster). Wisenheimer, with mock German or Yiddish surname suffix, first recorded 1904.

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