英语词源字典 - 在线词源网站

Betsy [Betsy 词源字典]: fem. pet name, a diminutive of Bet, itself short for Elizabet or Elizabeth. Betsy as the typical a pet name for a favorite firearm is attested in American English by 1856 (compare Brown Bess, by 1785, British army slang for the old flintlock musket).[Betsy etymology, Betsy origin, 英语词源]
brown (adj.): Old English brun "dark, dusky," developing a definite color sense only 13c., from Proto-Germanic *brunaz (cognates: Old Norse brunn, Danish brun, Old Frisian and Old High German brun, Dutch bruin, German braun), from PIE *bher- (3) "shining, brown" (cognates: Lithuanian beras "brown"), related to *bheros "dark animal" (compare beaver, bear (n.), and Greek phrynos "toad," literally "the brown animal").

The Old English word also had a sense of "brightness, shining," preserved only in burnish. The Germanic word was adopted into Romanic (Middle Latin brunus, Italian and Spanish bruno, French brun). Brown Bess, slang name for old British Army flintlock musket, first recorded 1785.
firelock (n.): type of gun lock that uses sparks to ignite the priming, 1540s, from fire (n.) + lock (n.). Originally of the wheel-lock; transferred 17c. to the flintlock.
flint-lock (n.): also flintlock, 1680s as a type of gunlock in which fire is produced by a flint striking the hammer, from flint + lock (n.1).
fusil (n.): flintlock musket, 1670s, from French fusil "musket" (see fusilier). Originally in English as distinguished from the matchlock variety.