bristle noun. › [C] a ​short, ​stiff ​hair, usually one of many: The ​old woman had a few ​grey bristles ​sprouting from her ​chin. › [C or U] The bristles of a ​brush are the ​stiff ​hairs or ​pieces of ​plastic that are ​connected to it: The ​best ​quality men's ​shaving ​brushes are made from ​badger bristle.