Tachometers are instruments that are often used for measuring the speed of an object or a system. However, there are many synonyms for the word tachometers that can be used to describe these instruments. Some of the most common synonyms include speedometers, RPM meters, rev counters, and engine gauges. Each of these terms refers to an instrument that measures the speed or rotational speed of a particular object or system. Additionally, these synonyms can be used in a variety of contexts, including automotive, aviation, and industrial applications. Overall, tachometers and their various synonyms provide important data and information in a range of settings.