gadgetyoudaoicibaDictYouDict[gadget 词源字典]
gadget: [19] Gadget is an elusive sort of word, as vague in its history as it is unspecific in its meaning. It seems to have originated as a piece of sailors’ slang, and is said to have been current as long ago as the 1850s, but the earliest record of it in print is from 1886, in R Brown’s Spun Yarn and Spindrift: ‘Then the names of all the other things on board a ship! I don’t know half of them yet; even the sailors forget at times, and if the exact name of anything they want happens to slip from their memory, they call it a chickenfixing, or a gadjet, or a gill-guy, or a timmeynoggy, or a wim-wom – just pro tem., you know’.

As for its source, suggestions have included French gâchette ‘catch of a mechanism’ and French dialect gagée ‘tool’.
[gadget etymology, gadget origin, 英语词源]
gadget (n.)youdaoicibaDictYouDict
1886, gadjet (but said by OED corespondents to date from 1850s), sailors' slang word for any small mechanical thing or part of a ship for which they lacked, or forgot, a name; perhaps from French gâchette "catch-piece of a mechanism" (15c.), diminutive of gâche "staple of a lock." OED says derivation from gauge is "improbable."