tachometer
noun
ta·chom·e·ter ta-ˈkä-mə-tər 
tə-
: a device for indicating speed of rotation
Did you know?
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.
Example Sentences
Recent Examples on the Web An analog speedometer and tachometer frame a small but easy-to-read 4.2-inch info display. 
Greg Fink, Car and Driver, 25 Apr. 2022 The modes, which change colors of the tachometer, adjust the level of steering assist and damping for sportier handling. Tribune News Service, cleveland, 30 July 2022 Hurtling into the triple digits, the McLaren makes the landscape blurrier until the tachometer’s climb hovers near 8,000 rpm. Basemwasef, Robb Report, 28 July 2022 The powerplant is relatively quiet, and its temperament is subdued – a continuous reassuring growl only notes its existence as the engine stays on the lower side of the tachometer. Michael Harley, Forbes, 2 June 2022 Other details include retro-style numerals and needles on the tachometer and sport chrono clock, embossed headrests, unique door-sill plates and leather upholstery on the sun visors, steering column and air-vent slats. Michael Harley, Robb Report, 27 Apr. 2022 The instrument panel cluster may not properly illuminate telltales or gauges and the speedometer and tachometer pointers. USA TODAY, 24 June 2022 The instrument cluster display has a large tachometer in the center flanked by smaller analog gauges on either side. Sam Abuelsamid, Forbes, 16 May 2022 Both the tachometer and dash-mounted clock of the standard Sport Chrono package include white needles set against faces with green numerals and accents, while Porsche embosses logos into the headrests and center-console lid. Greg Fink, Car and Driver, 27 Apr. 2022 See More
Greg Fink, Car and Driver, 25 Apr. 2022 The modes, which change colors of the tachometer, adjust the level of steering assist and damping for sportier handling. Tribune News Service, cleveland, 30 July 2022 Hurtling into the triple digits, the McLaren makes the landscape blurrier until the tachometer’s climb hovers near 8,000 rpm. Basemwasef, Robb Report, 28 July 2022 The powerplant is relatively quiet, and its temperament is subdued – a continuous reassuring growl only notes its existence as the engine stays on the lower side of the tachometer. Michael Harley, Forbes, 2 June 2022 Other details include retro-style numerals and needles on the tachometer and sport chrono clock, embossed headrests, unique door-sill plates and leather upholstery on the sun visors, steering column and air-vent slats. Michael Harley, Robb Report, 27 Apr. 2022 The instrument panel cluster may not properly illuminate telltales or gauges and the speedometer and tachometer pointers. USA TODAY, 24 June 2022 The instrument cluster display has a large tachometer in the center flanked by smaller analog gauges on either side. Sam Abuelsamid, Forbes, 16 May 2022 Both the tachometer and dash-mounted clock of the standard Sport Chrono package include white needles set against faces with green numerals and accents, while Porsche embosses logos into the headrests and center-console lid. Greg Fink, Car and Driver, 27 Apr. 2022 See More Word History
Etymology
Greek tachos speed + English -meter
First Known Use
1810, in the meaning defined above