The una corda pedal is a device on the piano that softens the sound of the instrument. There are several synonyms for this term, including "soft pedal", "una corde", and "left pedal". The soft pedal is the most commonly used synonym, as it accurately describes its function - to make the sound of the piano softer. Una corde, which means "one string" in Italian, refers to the fact that when the pedal is pressed, the hammer only strikes one string instead of the usual three, resulting in a softer sound. The term "left pedal" is used because it is the pedal located on the left side of the piano.