jam on the brake(s) | jam the brake(s) onidiomPart ofbrakejam on the brake(s) | jam the brake(s) onjam on the brake(s) | jam the brake(s) on — idiomidiom1. To press the brake pedal of a vehicle very hard and quickly.1.idiomDefinitionTo press the brake pedal of a vehicle very hard and quickly.ExampleMaya jammed on the brakes when a dog ran into the street.Did you jam the brakes on when you saw the red light?