Etymology
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Missouri 

originally a name for a group of native peoples among Chiwere (Siouan) tribes, from an Algonquian word recorded c. 1700, said to mean literally "people of the big canoes." Formed as a U.S. territory in 1812 (out of the whole of the Louisiana Purchase not admitted that year as the state of Louisiana); admitted as a state 1821.

In U.S. history, the Missouri Compromise (1820) in Congress admitted Missouri as a slave state, along with Maine as a free one, but set a line westward from the main southern boundary of Missouri above which no new states would be admitted with slavery. The expression I'm from Missouri, you'll have to show me is attested from at least c. 1880. Related: Missourian.

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Midwest (n.)

1926 in the U.S. geographical sense, from earlier Midwestern (1889) in reference to a group of states originally listed as West Virginia, Kentucky, Tennessee, Missouri, Kansas, and Arkansas; it now generally refers to states somewhat north and west of these (according to the U.S. Census Bureau, Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, South Dakota, and Wisconsin). Related: Midwesterner.

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Osage 

name of a group of Siouxan tribes originally from Missouri, 1690s, via French, from their self-designation Wazhazhe. The ornamental tree osage orange (Toxylon pomiferum), is attested by that name by 1817; it was originally found in and around their country.

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rickey (n.)

alcoholic drink made with carbonated water and lime juice, 1895, American English; in contemporary sources reputedly from the name of "Colonel" Joseph K. Rickey (1842-1903) of Callaway County, Missouri, Democratic lobbyist and wire-puller, who is said to have concocted it to entertain political friends.

And as long as there is thirst and limes, or lemons and gin, so long will the Honorable Joe Rickey be remembered in Missouri and his famous beverage tickle the palates of discriminating citizens. A hundred summers hence Joe Rickey will be called and Champ Clark and DeArmond forgotten. [The Conservative, Nebraska City, Neb., July 6, 1899.]
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muddy (adj.)

late 13c., in place names, "abounding in or covered with mud," from mud + -y (2). Meaning "not clear or pure in color" is from 1580s; extended to sounds by 1960s. Big Muddy as a nickname for the Missouri or Mississippi river is attested by 1825. Related: Muddily; muddiness.

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puke (n.)

1737, "a medicine which excites vomiting;" by 1938 as "material thrown up in vomiting," from puke (v.). U.S. colloquial meaning "native of Missouri" (1835) might be a different word, of unknown origin.

It is well known, that the inhabitants of the several western States are called by certain nicknames. Those of Michigan are called wolverines; of Indiana, hooshers; of Illinois, suckers; of Ohio, buckeyes; of Kentucky, corn-crackers; of Missouri pukes, &c. To call a person by his right nickname, is always taken in good part, and gives no offence; but nothing is more offensive than to mis-nickname—that is, were you to call a hoosher a wolverine, his blood would be up in a moment, and he would immediately show fight. [A.A. Parker, "Trip to the West and Texas," Concord, N.H., 1835]

Bartlett (1859) has "A nickname for a native of Missouri" as the second sense of puke (n.), the first being "A mean, contemptible fellow." The association of the state nickname with the "vomit" word is from at least 1858, and folk etymology talks of the old state literally vomiting forth immigrants to California.

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buster (n.)
1838, "anything large or exceptional; a man of great strength," American English slang (originally Missouri/Arkansas), perhaps meaning something that takes one's breath away and thus an agent noun from bust (v.). Around the same years, buster (as an extended form of bust (n.)) also meant "a frolic, a spree," hence "a roistering blade" (OED's definition, probably not the way they would have explained it in old Missouri and Arkansas), which might have influenced it. As a generic or playful address to a male from 1948, American English. Meaning "horse-breaker" is from 1891, American English; hence the back-formed verb bust (v.) "break a horse."
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butte (n.)
"conspicuous elevation," especially a steep-sided one notable in its isolation, 1805, American English, from French butte, from Old French but "mound, knoll; target to shoot at" (see butt (n.3)). A relic of the French exploration of the upper Missouri region, introduced in English in Lewis & Clark's journals.
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Plains (n.)

"lands of the American Midwest lying from roughly to the 104th meridian to the eastern slopes of the Rockies," 1755 (in singular form from 1680s), see plain (n.). Plains Indian is attested from 1844.

This region has a gradual slope from the mountains to the Missouri and Mississippi rivers, but is nowhere broken by any conspicuous ranges of hills. It is a region of small precipitation, wooded only along the banks of the streams, and not always there. The Plains and the prairies are not properly the same, from either a geographical or a climatological point of view. [Century Dictionary]
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vigilante (n.)
"member of a vigilance committee," 1856, American English, from Spanish vigilante, literally "watchman," from Latin vigilantem (nominative vigilans) "watchful, anxious, careful," from vigil "watchful, awake" (from PIE root *weg- "to be strong, be lively"). Vigilant man in same sense is attested from 1824 in a Missouri context. Vigilance committees kept informal rough order on the U.S. frontier or in other places where official authority was imperfect.
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