Etymology
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alacrity (n.)
"liveliness, briskness," mid-15c., from Latin alacritatem (nominative alacritas) "liveliness, ardor, eagerness," from alacer (genitive alacris) "cheerful, brisk, lively;" a word of uncertain origin. Perhaps cognate with Gothic aljan "zeal," Old English ellen "courage, zeal, strength," Old High German ellian. But de Vaan suggests the root sense is "to wander, roam" and a possible connection with ambulare.
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allegro 
1721 as a musical term, from Italian allegro "brisk, sprightly, cheerful," from Latin alacrem (nominative alacer) "lively, cheerful, brisk" (see alacrity). The same Latin word came into English 17c. as aleger "lively, brisk," from Old French alegre, from Latin Related: alacris; and Milton used "L'Allegro" in its literal sense as a poem title (1632).
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quickness (n.)

c. 1200, quiknesse, "state of being alive," from quick (adj.) + -ness. Early 15c. as "alacrity, speed, rapidity;" mid-15c. as "readiness of perception, keenness of mind."

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shebang (n.)

1862 (Whitman), "hut, shed, shelter," American English slang, popularized among soldiers in the U.S. Civil War, but like much of the soldier's slang (e.g. skedaddle, shoddy), it is of uncertain origin.

Perhaps it is an alteration of shebeen (q.v.), but shebang meaning "tavern," a seemingly necessary transitional sense, is not attested before 1878 and shebeen seems to have been not much used in the U.S. Bartlett's 1877 edition describes shebeen as "A strange word that had its origin during the late civil war. It is applied alike to a room, a shop, or a hut, a tent, a cabin; an engine house."

The phrase the whole shebang is recorded from 1869, but its relation to the earlier use of the word is obscure. Either or both senses also might be mangled pronunciations of French char-à-banc, a bus-like wagon with many seats. For an older guess:

[Shebang] used even yet by students of Yale College and elsewhere to designate their rooms, or a theatrical or other performance in a public hall, has its origin probably in a corruption of the French cabane, a hut, familiar to the troops that came from Louisiana, and constantly used in the Confederate camp for the simple huts, which they built with such alacrity and skill for their winter quarters. The constant intercourse between the outposts soon made the term familiar to the Federal army also. ["Americanisms: The English of the New World," Maximillian Schele De Vere, New York, Charles Scribner & Co., 1872.]
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