Etymology
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air force (n.)
1917, from air (n.1) + force (n.); first attested with creation of the Royal Air Force. There was no United States Air Force until after World War II. The Air Corps was an arm of the U.S. Army. In 1942, the War Department reorganized it and renamed it Army Air Forces. The National Security Act of 1947 created the Department of the Air Force, headed by a Secretary of the Air Force, and the U.S.A.F.
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static (adj.)
1630s, "pertaining to the science of weight and its mechanical effects," from Modern Latin statica, from Greek statikos "causing to stand, skilled in weighing," from stem of histanai "to make to stand, set; to place in the balance, weigh," from PIE root *sta- "to stand, make or be firm." Earlier statical (1560s). The sense of "having to do with bodies at rest or with forces that balance each other" is first recorded 1802. Applied to frictional electricity from 1839.
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chevalier (n.)

late 14c. (c. 1200 as a surname), "mounted knight, armed horseman of noble birth," from Anglo-French chivaler "mounted knight," Old French chevalier "knight, horseman, knight in chess" (12c., Modern French chevaler), from Late Latin caballarius "horseman" (source of Provençal cavallier, Spanish caballero, Portuguese cavalleiro, Italian cavaliere; see cavalier (n.)). The word was nativized in Middle English ("chevaleer"), but has been given a French pronunciation since 16c.

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stour (n.)
c. 1300, "tumult, armed conflict, struggle with adversity or pain," from Anglo-French estur, Old French estour "a tumult, conflict, assault, shock, battle," from Proto-Germanic *sturmaz "storm" (source also of Old High German sturm "storm; battle;" see storm (n.)). Became obsolete, revived by Spenser and his followers in various senses; also surviving as a Scottish and Northern English word meaning "a (driving) storm" or "uproar, commotion." Italian stormo also is from Germanic.
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wapentake (n.)
division of certain English counties (equivalent to a hundred in other places), Old English wæpengetæc "division of a riding," from Old Norse vapnatak, from vapna, genitive plural of vapn "weapon" (see weapon) + tak "a touching, a taking hold, a grasping," from taka "to take, grasp," from Proto-Germanic *tak- (see take (v.)). Perhaps it originally was an armed muster with inspection of weapons, or else an assembly where consent was expressed by brandishing swords and spears.
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happy (adj.)
Origin and meaning of happy

late 14c., "lucky, favored by fortune, being in advantageous circumstances, prosperous;" of events, "turning out well," from hap (n.) "chance, fortune" + -y (2). Sense of "very glad" first recorded late 14c. Meaning "greatly pleased and content" is from 1520s. Old English had eadig (from ead "wealth, riches") and gesælig, which has become silly. Old English bliðe "happy" survives as blithe. From Greek to Irish, a great majority of the European words for "happy" at first meant "lucky." An exception is Welsh, where the word used first meant "wise."

Happy medium "the golden mean" is from 1702. Happy ending in the literary sense recorded from 1756. Happy as a clam (1630s) was originally happy as a clam in the mud at high tide, when it can't be dug up and eaten. Happy hunting ground, the reputed Native American paradise, is attested from 1840, American English. Happy day for "wedding day" is by 1739; happy hour for "early evening period of discount drinks and free hors-d'oeuvres at a bar" is by 1961, said to be 1950s. Rock-happy (1945) was U.S. Pacific theater armed forces slang for "mentally unhinged after too much time on one island." Related: Happier; happiest.

Happy family an assemblage of animals of diverse habits and propensities living amicably, or at least quietly, together in one cage. [Century Dictionary]
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trajectory (n.)
"path described by a body moving under the influence of given forces," 1690s, from Modern Latin trajectorium, from trajectorius "of or pertaining to throwing across," from Latin traiectus "thrown over or across," past participle of traicere "throw across, shoot across," from Latin trans "across, beyond" (see trans-) + icere, combining form of iacere "to throw" (from PIE root *ye- "to throw, impel"). Middle French and Middle English had trajectorie as "end of a funnel," from Latin traiectorium.
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battle (n.)

"fight or hostile engagement between opposing forces," c. 1300, from Old French bataille "battle, single combat," also "inner turmoil, harsh circumstances; army, body of soldiers," from Late Latin battualia "exercise of soldiers and gladiators in fighting and fencing," from Latin battuere "to beat, to strike" (see batter (v.)).

Battle-cry is from 1812; battle-flagfrom 1840; battle-scarred is from 1848. Phrase battle royal "fight involving several combatants" is from 1670s.

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doolally (adj.)
"insane, eccentric," British slang, by 1917 in the armed services and in full doolally tap (with the Urdu word for "fever"), from Deolali, near Bombay, India, which was a military camp (established 1861) with a large barracks and a chief staging point for British troops on their way to or from India; the reference is to men whose enlistments had expired who waited there impatiently for transport home.
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squad (n.)

1640s, "small number of military men detailed for some purpose," from French esquade, from French escadre, from Spanish escuadra or Italian squadra "battalion," literally "square," from Vulgar Latin *exquadra "to square," from Latin ex "out" (see ex-) + quadrare "make square," from quadrus "a square" (from PIE root *kwetwer- "four"). Before the widespread use of of automatic weapons, infantry troops tended to fight in a square formation to repel cavalry or superior forces. Extended to sports 1902, police work 1905.

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