To thrash means to beat or strike something violently and repeatedly. When a fish is pulled from water, it might thrash wildly, whipping its body back and forth trying to escape. A swimmer caught in rough ocean waves gets thrashed around, tossed and tumbled by the powerful water.

The word also describes defeating someone thoroughly in a competition. When one soccer team thrashes another 8-0, they don't just win: they dominate completely. You might say your friend thrashed you at chess when they captured your pieces one after another and checkmated you quickly.

Thrashing can mean struggling with violent, uncontrolled movements. A person having a nightmare might thrash in bed, arms and legs flailing. When you thrash about in frustration, you're moving aggressively without much control or purpose.

In farming, threshing (sometimes spelled thrashing) means separating grain from stalks by beating it, though this older agricultural meaning is less common in everyday conversation. The violent, repetitive beating motion connects all these uses of the word.