Etymology
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cracker (n.1)

mid-15c., "hard wafer," but the specific application to a thin, crisp biscuit is by 1739; literally "that which cracks or breaks," agent noun from crack (v.). Meaning "instrument for crushing or cracking" is from 1630s.

Coal-cracker is from 1853 of persons, 1857 of machinery that breaks up mined coal. Cracker-barrel (1861) "barrel full of soda-crackers for sale" was such a common feature of old country stores that the phrase came to be used by 1905 as an adjective, "emblematic of down-home ways and views."

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cracker (n.2)

Southern U.S. derogatory term for "poor, white trash" (1766), probably an agent noun from crack (v.) in the sense "to boast" (as in not what it's cracked up to be). Cracker "a boaster, a braggart" is attested from c. 1500; also see crack (n.). Compare Latin crepare "to rattle, crack, creak," with a secondary figurative sense of "boast of, prattle, make ado about."

I should explain to your Lordship what is meant by crackers; a name they have got from being great boasters; they are a lawless set of rascalls on the frontiers of Virginia, Maryland, the Carolinas and Georgia, who often change their places of abode. [letter from colonial officer Gavin Cochrane to the Earl of Dartmouth, June 27, 1766]

But DARE compares corn-cracker "Kentuckian," also "poor, low-class white farmer of Georgia and North Carolina" (1835, U.S. Midwest colloquial).

The word was used especially of Georgians by 1808, though often extended to residents of northern Florida. Another name in mid-19c. use was sand-hiller "poor white in Georgia or South Carolina."

Not very essentially different is the condition of a class of people living in the pine-barrens nearest the coast [of South Carolina], as described to me by a rice-planter. They seldom have any meat, he said, except they steal hogs, which belong to the planters, or their negroes, and their chief diet is rice and milk. "They are small, gaunt, and cadaverous, and their skin is just the color of the sand-hills they live on. They are quite incapable of applying themselves steadily to any labor, and their habits are very much like those of the old Indians." [Frederick Law Olmsted, "A Journey in the Seaboard Slave States," 1856]
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wisecrack (n.)
1906, American English, from wise (adj.) + crack in the "boast" sense (see cracker (n.2)). As a verb from 1915. Related: Wisecracking.
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sand-hill (n.)

"dune," Old English sondhyllas (plural); see sand (n.) + hill (n.). For sand-hiller "poor white of Georgia or South Carolina" (by 1848) see cracker (n.2). Earlier it meant "blackguard, user of foul language" (by 1813) in the dialect of Durham and Yorkshire, according to contemporary sources probably from Sandhill in Newcastle.

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nut-cracker (n.)

also nutcracker, "instrument used for cracking hard-shelled nuts," 1540s, from nut (n.) + agent noun from crack (v.). Hence also "toy having a grotesque human head, in the mouth of which a nut is placed to be cracked by a screw or lever." The ballet was first performed in 1892, based on Dumas père's rendition of E.T.A. Hoffmann's 1816 story "Nussknacker und Mausekönig."

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cracker-jack (n.)

also crackerjack, "something excellent," 1893, U.S. colloquialism, apparently a fanciful construction, earliest use in reference to racing horses. The caramel-coated popcorn-and-peanuts confection was said to have been introduced at the World's Columbian Exposition (1893). Supposedly a salesman gave it the name when he tasted some and said, "That's a cracker-jack," using the then-popular expression. The name was trademarked 1896. The "Prize in Every Box" was introduced 1912.

"Your brother Bob is traveling, isn't he?"
"Yep. He's with one of the big racing teams. I tell you, he's a cracker-jack! Wins a bushel of diamonds and gold cups every week."
[Life magazine, Aug. 1, 1895]
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saltine (n.)
"salted flat cracker," 1907, short for saltine cracker (1894), from salt (n.) + -ine (1).
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Triscuit (n.)
proprietary name for a type of cracker, 1906, curiously from tri- + biscuit.
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firecracker (n.)

also fire-cracker, "exploding paper cylinder," 1830, American English coinage for what is in England a cracker, but the U.S. word distinguishes it from the word meaning "biscuit." See fire (n.) + agent noun from crack (v.).

Sec 2 And be it enacted, That it shall not be lawful for any person to burn, explode or throw any burning fire cracker, squib, turpentine balls or fire serpents in this state. [act of the General Assembly of the state of New Jersey, Feb. 18, 1835]
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safecracker (n.)
also safe-cracker, 1897, from safe (n.) + agent noun from crack (v.). Originally in reference to thieves who used dynamite.
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