1. a cylindrical part that moves up and down inside a cylinder in an engine or pump

Examples

• The car’s engine has six pistons that move rapidly up and down.
• A damaged piston can cause serious engine problems.
• The mechanic replaced the worn piston rings.
• Steam engines use pistons to convert steam pressure into motion.
• The hydraulic pump’s piston creates pressure to lift heavy objects.
• Each piston is connected to the crankshaft by a connecting rod.