appliance, contraption, contrivance, convenience, gadget, gizmo, gismo, widget

a device that very useful for a particular job

• gadgetry — appliances collectively
• gimbals — an appliance that allows an object (such as a ship's compass) to remain horizontal even as its support tips
• injector — a contrivance for injecting (e.g., water into the boiler of a steam engine or particles into an accelerator etc.)
• mod con — (British) modern convenience; the appliances and conveniences characteristic of a modern house

• device — an instrumentality invented for a particular purpose