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A tachometer is literally a "speed-measurer", since the Greek root tach- means "speed". This is clear in the names of the tachyon, a particle of matter that travels faster than the speed of light (if it actually exists, it's so fast that it's impossible to see with any instrument), and tachycardia, a medical condition in which the heart races uncontrollably. Since the speed that an auto tachometer measures is speed of rotation of the crankshaft, the numbers it reports are revolutions per minute, or rpm's.
Examples of tachometer in a Sentence
Michael Van Runkle, Robb Report, 2 Nov. 2024
Alfa spotters will easily distinguish the 1750 and 2000 GTVs by their four headlamps and the interior’s larger twin tachometer and speedometer.
—Robert Ross, Robb Report, 11 Oct. 2024
But edge deeper into the throttle and that small block wakes up, clearly preferring the higher end of the tachometer.
—Michael Van Runkle, Robb Report, 18 Sep. 2024
Jonathan Gitlin Here, the N E-Shift button has been pressed, and the power gauge on the right has turned into a tachometer.
—Jonathan M. Gitlin, Ars Technica, 6 Sep. 2024
See all Example Sentences for tachometer 
Dictionary Entries Near tachometer
Cite this Entry
“Tachometer.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/tachometer. Accessed 30 Nov. 2024.
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tachometer
noun
from Greek tachos "speed" and English meter "an instrument for measuring"
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