Etymology
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firelock (n.)

type of gun lock that uses sparks to ignite the priming, 1540s, from fire (n.) + lock (n.1). Originally of the wheel-lock; transferred 17c. to the flintlock.

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mainspring (n.)

1590s, "principal spring of a mechanism" (of a watch, clock, gun, etc.), from main (adj.) + spring (n.3). Figurative meaning "impelling cause or motive of any action" is from 1690s.

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shotgun (n.)

"gun made for firing small shot," 1821, American English, from shot (n.) in the sense of "lead in small pellets" (1770) + gun (n.).

In later use implying a smooth-bore gun as distinguished from a rifle, which fires bullets. Typically used for hunting small animals, etc. Included in "etc." is the image in shotgun wedding, a partially figurative phrase attested by 1903 in American English. Shotgun in reference to a house, shack, or other building with rooms all opening into a long, central hall is by 1938, probably so called from this arrangement. To ride shotgun is by 1905, from custom of having an armed man beside the driver on the stagecoach in the Old West to ward off trouble. The U.S. football offensive shotgun formation is attested by 1966.

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bore (n.1)

Old English bor "instrument for making holes by boring or turning," from the source of bore (v.1). As "hole made by boring," early 14c. The meaning "cylindrical hole through a tube, gun, etc." is from 1570s; that of "interior diameter of a tube, caliber of a gun" (whether bored or not) is from 1580s. Hence figurative slang full bore (1936) "at maximum speed," from notion of unchoked carburetor on an engine.

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reload (v.)

also re-load, "to load again, as a ship, etc.," 1778, from re- "back, again" + load (v.). Of a firearm or gun, by 1789. Related: Reloaded; reloading.

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gunwale (n.)

"uppermost edge of a ship's side," mid-15c., gonne walle, from gun (n.) + wale "plank" (see wale). Originally a platform on the deck of a ship to support the mounted guns.

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ack 

British oral code for letter -a- in wireless and telephone communication, 1898; hence ack-ack "anti-aircraft" (gun, fire, etc.). Compare toc (-t-), emma (-m-).

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choke (n.)

1560s, "quinsy," from choke (v.). Meaning "action of choking" is from 1839. Meaning "valve which controls air to a carburetor" first recorded 1926; earlier it meant "constriction in the bore of a gun" (1875).

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knockout (n.)

also knock-out, in fighting, 1887, from verbal phrase knock out "to stun by a blow for a 10-count" in boxing, short for to knock out of time; see knock (v.) + out (adv.). Slang meaning "excellent thing or person" is from 1892; specifically "beautiful woman" by 1953. As an adjective from 1896 in the tournament competition sense, 1898 in fighting. To knock oneself out "make a great effort" is from 1936.

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limber (v.)

"make pliant or supple," 1748, from limber (adj.). Related: Limbered; limbering. With up (adv.) by 1901. The military sense "attach a limber to a gun" (1783) is from limber (n.).

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