Piston (noun)

1. A cylindrical part in an engine or pump that moves up and down to transfer pressure and force from a fluid or gas to a crankshaft or other mechanism.
2. A rod or cylinder that fits tightly in a tube and is moved by or moves against pressure, typically to transmit or measure the pressure of a fluid.

Origin:

Early 17th century: from french piste "pestle" (because the original pistons were rod-shaped), from latin pistillum "pestle".

Examples:

1. The engine's pistons were worn out and needed to be replaced.
2. The air compressor uses a piston to compress the air.
3. He checked the oil level by looking at the dipstick on the piston.
4. The syringe uses a piston to draw in liquid.
5. The pistons in the engine were oiled to reduce friction.