Etymology
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smart (adj.)
late Old English smeart "painful, severe, stinging; causing a sharp pain," related to smeortan (see smart (v.)). Meaning "executed with force and vigor" is from c. 1300. Meaning "quick, active, clever" is attested from c. 1300, from the notion of "cutting" wit, words, etc., or else "keen in bargaining." Meaning "trim in attire" first attested 1718, "ascending from the kitchen to the drawing-room c. 1880" [Weekley]. For sense evolution, compare sharp (adj.).

In reference to devices, the sense of "behaving as though guided by intelligence" (as in smart bomb) first attested 1972. Smarts "good sense, intelligence," is first recorded 1968 (Middle English had ingeny "intellectual capacity, cleverness" (early 15c.)). Smart cookie is from 1948.
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nerve (n.)

late 14c., nerve, nerf, "sinew, tendon, hard cord of the body" (a sense now obsolete), also "fiber or bundle of fibers that convey the capacity to feel or move from the brain or spinal cord to the body," from Old French nerf and directly from Medieval Latin nervus "a nerve," from Latin nervus "sinew, tendon; cord, bowstring, string of a musical instrument," metathesis of pre-Latin *neuros, from PIE *(s)neu- "tendon, sinew" (source also of Sanskrit snavan- "band, sinew," Armenian neard "sinew," Greek neuron "sinew, tendon," in Galen "nerve").

The late medieval surgeons understood the nature and function of the nerves and often used nervus to denote a `nerve' in the modern sense, as well as to denote a `tendon'. There appears to have been some confusion, however, between nerves and tendons; hence, a number of instances in which nervus may be interpreted in either way or in both ways simultaneously. [Middle English Compendium] 

The secondary senses developed from meaning "strength, vigor; force, energy" (c. 1600), from the "sinew" sense. Hence the non-scientific sense with reference to feeling or courage, first attested c. 1600 (as in nerves of steel, 1869) and that of "coolness in the face of danger, fortitude under trying or critical circumstances" is by 1809. The bad sense "impudence, boldness, cheek" (originally slang) is by 1887. Latin nervus also had a figurative sense of "vigor, force, power, strength," as did Greek neuron. From the neurological sense come Nerves "condition of hysterical nervousness," attested by 1890, perhaps from 1792. To get on (someone's) nerves is from 1895. War of nerves "psychological warfare" is from 1915.

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crazy (adj.)

1570s, "diseased, sickly" (a sense now obsolete); 1580s, "broken, impaired, full of cracks or flaws," from craze + -y (2). Meaning "deranged, demented, of unsound mind or behaving as so" is from 1610s. Jazz slang sense "cool, exciting" is attested by 1927. Related: Crazily; craziness.

To drive (someone) crazy is attested by 1873. To do something like crazy "with manic vigor or frequency" is by 1905. Phrase crazy like a fox has origins by 1935. Crazy Horse, name of the Teton Lakhota (Siouan) war leader (d. 1877), translates thašuka witko, literally "his horse is crazy." Crazy-quilt (1886) preserves the original "break to pieces" sense of craze (v.). Crazy bone as an alternative to funny bone is recorded by 1853.

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youth (n.)

Old English geoguð "youth; young people, junior warriors; young of cattle," related to geong "young," from Proto-Germanic *jugunthi- (source also of Old Saxon juguth, Old Frisian jogethe, Middle Dutch joghet, Dutch jeugd, Old High German jugund, German Jugend, Gothic junda "youth"), from suffixed form of PIE root *yeu- "vital force, youthful vigor" (see young (adj.)) + Proto-Germanic abstract noun suffix *-itho (see -th (2)).

According to OED, the Proto-Germanic form apparently was altered from *juwunthiz by influence of its contrast, *dugunthiz "ability" (source of Old English duguð). In Middle English, the medial -g- became a yogh, which then disappeared.

They said that age was truth, and that the young
Marred with wild hopes the peace of slavery
[Shelley]
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nervous (adj.)

late 14c., "containing nerves; affecting the sinews" (the latter sense now obsolete); from Latin nervosus "sinewy, vigorous," from nervus "sinew, nerve" (see nerve (n.)). The meaning "of or belonging to the nerves" in the modern anatomical sense is from 1660s.

From 1630s it was used (of writing style, etc.) in the sense of "possessing or manifesting vigor of mind, characterized by force or strength." But the opposite meaning "suffering disorder of the nervous system" is from 1734, hence the illogical sense "restless, agitated, lacking nerve, weak, timid, easily agitated" (1740). This and its widespread popular use as a euphemism for mental forced the medical community to coin neurological to replace nervous in the older sense "pertaining to the nerves." Nervous wreck first attested 1862; nervous breakdown 1866. Related: Nervously; nervousness.

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young (adj.)

Old English geong "youthful, young; recent, new, fresh," from Proto-Germanic *junga- (source also of Old Saxon and Old Frisian jung, Old Norse ungr, Middle Dutch jonc, Dutch jong, Old High German and German jung, Gothic juggs), from PIE *yuwn-ko-, suffixed form of root *yeu- "vital force, youthful vigor" (source also of Sanskrit yuvan- "young; young man;" Avestan yuuanem, yunam "youth," yoista- "youngest;" Latin juvenis "young," iunior "younger, more young;" Lithuanian jaunas, Old Church Slavonic junu, Russian junyj "young," Old Irish oac, Welsh ieuanc "young").

From c. 1830-1850, Young France, Young Italy, etc., were loosely applied to "republican agitators" in various monarchies; also, especially in Young England, Young America, used generally for "typical young person of the nation." For Young Turk, see Turk.

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junior (adj.)

late 13c., "younger, not as old as another," from Latin iunior "younger, more young," comparative of iuvenis "young; a young man," etymologically "one who possesses vital force" (from PIE root *yeu- "vital force, youthful vigor;" see young (adj.)).

Used after a person's name to mean "the younger of two" from late 13c. Abbreviation Jr. is attested from 1620s. Meaning "of lesser standing, more recent" is from 1766. That of "meant for younger people, of smaller size" is from 1860. Junior miss "young teenage girl" is from 1907. In U.S. colleges, "pertaining to the third-year." Junior college is attested by 1896; junior high school is from 1909.

The junior high school is rapidly becoming the people's high school. The percentage of pupils completing the ninth year is constantly rising where junior high schools have been established. [Anne Laura McGregor, "Supervised Study in English for Junior High School Grades," New York, 1921]
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prime (n.)

"earliest canonical hour of the day" (6 a.m.), from Old English prim and Old French prime and directly from Medieval Latin prima "the first service," from Latin prima hora "the first hour" (of the Roman day), from Latin primus "first, the first, first part" (see prime (adj.)).  (In classical Latin, the noun uses of the adjective meant "first part, beginning; leading place.")

By extension, "the first division of the day" 6 a.m. to 9 a.m. (early 13c.). The sense of "beginning of a period or course of events" is from late 14c. From the notion of "the period or condition of greatest vigor in life" (by 1530s) comes the specific sense "springtime of human life" (often meaning ages roughly 21 to 28) is from 1590s. Also from 1590s as "that which is best in quality, highest or most perfect state of anything." As "a prime number," by 1530s.

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virtue (n.)
Origin and meaning of virtue

c. 1200, vertu, "moral life and conduct; a particular moral excellence," from Anglo-French and Old French vertu "force, strength, vigor; moral strength; qualities, abilities" (10c. in Old French), from Latin virtutem (nominative virtus) "moral strength, high character, goodness; manliness; valor, bravery, courage (in war); excellence, worth," from vir "man" (from PIE root *wi-ro- "man").

For my part I honour with the name of virtue the habit of acting in a way troublesome to oneself and useful to others. [Stendhal "de l'Amour," 1822]

Especially (in women) "chastity, sexual purity" from 1590s. Phrase by virtue of (early 13c.) preserves alternative Middle English sense of "efficacy." Wyclif Bible has virtue where KJV uses power. The seven cardinal virtues (early 14c.) were divided into the natural (justice, prudence, temperance, fortitude) and the theological (hope, faith, charity). To make a virtue of a necessity (late 14c.) translates Latin facere de necessitate virtutem [Jerome].

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constitution (n.)
Origin and meaning of constitution

mid-14c., constitucioun, "law, regulation, edict; body of rules, customs, or laws," from Old French constitucion (12c.) "constitution, establishment," and directly from Latin constitutionem (nominative constitutio) "act of settling, settled condition, anything arranged or settled upon, regulation, order, ordinance," noun of state from past-participle stem of constituere "to cause to stand, set up, fix, place, establish, set in order; form something new; resolve" (see constitute).

Meaning "action of establishing, creation" is from c. 1400; that of "way in which a thing is constituted" is from c. 1600; that of "physical health, strength and vigor of the body" is from 1550s; of the mind, "temperament, character" from 1580s.

Sense of "mode of organization of a state" is from c. 1600; that of "system of fundamental principles by which a community is governed" dates from 1730s; since the 1780s especially of the fundamental principles and rules of a government as embodied in a written document (as in the U.S. and France). In reference to Britain, the word was a collective name for the fundamental principles established by the political development of the English people embodied in long-accepted precedents. 

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