speedometer

Etymology

speed + -o- + -meter

noun

1. An instrument located within the dashboard of a vehicle that measures and indicates the current speed of the vehicle.
   Although it might be thought that drivers would naturally refer constantly to the speedometer, older drivers who come to diesel driving after years of steam experience without the help of speedometers, as well as those on steam engines which have been equipped with speedometers in recent years, have not accustomed themselves to the constant use of this instrument. 1962 December, “Talking of Trains: Derailment at Lincoln”, in Modern Railways, page 375
2. Such a device incorporating an odometer.