A small mechanical or electronic device or tool, especially an ingenious or novel one. She always carries a handy gadget in her bag to help with unexpected tasks.
Computing: A small self-contained software application or widget that performs a specific function on a computer, website, or mobile interface. He installed a weather gadget on his phone to check the forecast.
Informal: Any object or device whose proper name is unknown or temporarily forgotten. Pass me that gadget over there—the one with the red handle.