speed·om·e·ter 
/spɪˈdɑ:mətɚ/ noun
plural speed·om·e·ters /spɪˈdɑ:mətɚ/ noun [count] : an instrument in a car, truck, etc., that indicates how fast the vehicle is going —called also (Brit) speedo /ˈspi:doʊ/; — see picture at car; compare odometer, tachometer
/ˈspi:doʊ/; — see picture at car; compare odometer, tachometer
