any of various instruments for measuring or indicating velocity or speed, as of a machine, a river, or the blood.
an instrument measuring revolutions per minute, as of an engine.
Origin of tachometer
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
any device for measuring speed, esp the rate of revolution of a shaft. Tachometers (rev counters) are often fitted to cars to indicate the number of revolutions per minute of the engine
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
1810, from Greek tachos "speed" + -meter.
Online Etymology Dictionary, © 2010 Douglas Harper
An instrument used to measure the rotations per minute of a rotating shaft.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.