Definitions:

1. A device that measures and displays the rotational speed of a shaft or disk, commonly used in vehicles to monitor engine speed. NOUN
   • A faulty tachometer can lead to inaccurate engine performance.
2. A measuring instrument used to indicate the speed of rotation of an engine or other rotating machine, typically measured in revolutions per minute. NOUN
   • Racing drivers keep an eye on the tachometer to avoid over-revving the engine.

Synonyms:

• odometer
• rpm
• speedometer
• tach