1) De-emphasize 2) Piano muter 3) Play down 4) Tone down 
The soft pedal (or una corda pedal) is one of the standard pedals on a piano, generally placed leftmost among the pedals. On a grand piano this pedal shifts the whole action including the keyboard slightly to the right, so that hammers which normally strike all three of the strings for a note strike only two of them. This softens the note and also...
[Verb] To tone something down.
(from the article `keyboard instrument`) ...all the dampers by the ordinary damper pedal. On three-pedal pianos, this device is included as the middle pedal, with the damper (`loud`) pedal ...
to rotate the pedals without actually applying power.
[n] - a pedal on a piano that moves the action closer to the strings and so soften the sound[v] - play down or obscure
noun a pedal on a piano that moves the action closer to the strings and so soften the sound
to rotate the pedals without actually applying power.
To pedal without much effort or coast.