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speedometer

[spee-dom-i-ter, spi-]

noun

an instrument on an automobile or other vehicle for indicating the rate of travel in miles or kilometers per hour.

Origin of speedometer

First recorded in 1900–05; speed + -o- + -meter
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
British Dictionary definitions for speedometer

speedometer

noun

a device fitted to a vehicle to measure and display the speed of travelSee also mileometer
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
Word Origin and History for speedometer
n.

1904, from speed + -meter. A Germanic-Greek hybrid and thus execrated by purists.

[T]he ancient Greeks & Romans knew what speed was, & yet no-one supposes they called it speed, whence it follows that speedo- & speedometer are barbarisms. [Fowler]
Online Etymology Dictionary, © 2010 Douglas Harper
speedometer in Science

speedometer

[spĭ-dŏm′ĭ-tər]

An instrument for indicating the speed of a vehicle, typically by measuring the rate of rotation of a wheel or fan whose rate of rotation depends on the speed of the vehicle. Compare odometer.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.