The American Heritage® Dictionary of the English Language, 4th edition Copyright © 2010 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
A machine that records the measurements of a tachometer, especially one in a vehicle recording its speed and the times at which it was driven.
Origin: Greek takhos, speed + -graph.