A gadget is a tool or device, especially one that works remarkably well for a specific task. Your dad's favorite kitchen gadget might be his special knife that cuts vegetables into spirals.
The remote control your brother rigs up to the Christmas tree is a gadget, and your camping tool that folds out into various knives, corkscrews, and scissors is another kind of gadget. The original spelling was gadjet, and it's thought to have originated in the 1850's as sailors' slang, meaning any mechanism or ship part that either lacked a name or whose name had been forgotten. It may be rooted in the French gâchette, "piece of a mechanism."