Tachometer (noun)

An instrument that measures the rotational speed of a machine, especially an internal combustion engine, typically in revolutions per minute.

Origin:

Late 19th century, from greek takhos 'speed' + -meter.

Examples:

1. The tachometer on the car's dashboard indicated that the engine was running smoothly.
2. The tachometer on the motorcycle showed that the rider was pushing the limits of the engine's capabilities.
3. The tachometer on the boat's console helped the skipper monitor the engine's performance.
4. The tachometer on the aircraft's instrument panel was an essential tool for the pilot.
5. The tachometer on the generator provided critical information for maintenance and operation.