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"small hand-held firearm," 1570s, from Middle French pistole "short firearm" (1566), of uncertain origin, sometimes said to be from German Pistole, from Czech pis'tala "firearm," literally "tube, pipe," from pisteti "to whistle," of imitative origin, related to Russian pischal "shepherd's pipe."
But earlier English form pistolet (1550) is said to be from Middle French pistolet "a small firearm," also "a small dagger," which may be the literal sense; though some connect this word with Italian pistolese, in reference to Pistoia, town in Tuscany noted for gunsmithing. Pistol-whip (v.) is first recorded 1942.
[first sense probably a euphemism for pisser; lunch-counter sense because the eater feels as if shot in the stomach soon after eating hot pastrami]
[IBM] A tool that makes it all too easy for you to shoot yourself in the foot. "Unix "rm *" makes such a nice pistol!"