The euphonium is a medium-sized, conical-bore, tenor-voiced brass instrument that derives its name from the Ancient Greek word εὔφωνος euphōnos, meaning "well-sounding" or "sweet-voiced" (εὖ eu means "well" or "good" and φωνή phōnē means "sound", hence "of good sound"). The euphonium is a valved instrument. Nearly all current models have piston valves, though some models with rotary valves do exist. The euphonium may be played in bass clef as a non-transposing instrument or in treble clef as a transposing instrument. In British brass bands, it is typically treated as a treble-clef instrument, while in American band music, parts may be written in either treble clef or bass clef, or both.