tachometer
ta.chom.e.ter \ta-'ka:m-*t-*r, t*-\ n [Gk tachos speed + E -meter] : a device for indicating speed of rotation
Webster's English Dictionaryta.chom.e.ter \ta-'ka:m-*t-*r, t*-\ n [Gk tachos speed + E -meter] : a device for indicating speed of rotation