musket
First attested around 1210 as a surname, and later in the 1400s as a word for the sparrowhawk (Middle English forms: musket, muskett, muskete (“sparrow hawk”)),[1][2] from Middle French mousquet, from Old Italian moschetto (a diminutive of mosca (“fly”), from Latin musca) used to refer initially to a sparrowhawk (given its small size or speckled appearance)[2] and then a crossbow arrow and later a musket,[2][3][4] adhering to a pattern of naming firearms and cannons after birds of prey and similar creatures (compare falcon, falconet),[2][4] a sense which was also borrowed into French and then (around 1580)[3] into English.[4] Cognate to Spanish mosquete, Portuguese mosquete.[4] Smoothbore firearms continued to be called muskets even as they switched from using matchlocks to flintlocks to percussion locks, but with the advent of rifled muskets, the word was finally displaced by rifle.[4]
rifle
Originally short for “rifled gun”, referring to the spiral grooves inside the barrel. From Middle English, from Old French rifler (“to scrape off, plunder”), from Old Dutch *riffilōn (compare archaic Dutch rijfelen (“to scrape”), Old English geriflian (“to wrinkle”)), frequentative of Proto-Germanic *rīfaną (compare Old Norse rífa (“to tear, break”)). More at rive.
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From Middle English riven (“to rive”), of North Germanic origin, from Old Norse rífa (“to rend, tear apart”), from Proto-Germanic *rīfaną (“to tear, scratch”), from Proto-Indo-European *h₁reyp- (“to crumble, tear”).
Cognate with Danish rive (“to tear”), Old Frisian rīva (“to tear”), Old English ārǣfan (“to let loose, unwrap”), Old Norse ript (“breach of contract, rift”), Norwegian Bokmål rive (“to tear”) and Albanian rrip (“belt, rope”). More at rift.
gun
From Middle English gunne, gonne, from Lady Gunilda, a huge crossbow with a powerful shot, with the second part of the term being of Old Norse origin. It was later used to denote firearms. The name Gunnhildr and its multiple variations are derived from Old Norse gunnr (“battle, war”) + hildr (“battle”), which makes it a pleonasm. In the given context the woman's name means battle maid. See also Hilda, Gunilda, Gunhild, Gunhilda, Gunnhildr.
pistol
Probably from Middle French pistole, which probably via Middle High German forms like pischulle from Czech píšťala (“firearm”, literally “tube, pipe”),[1] from Proto-Slavic *piščalь, from *piskati, *piščati (“to squeak, whistle”), from Proto-Balto-Slavic *pīṣk-.
Alternatively, from Middle English pistolet, from Middle French pistolet (“small firearm or small dagger”), from or related to Italian pistolese (“short dagger”), from Italian Pistoia (“a Tuscan town noted for its gunsmithing”).