WordNet (r) 3.0 (2006):

soft pedal
    n 1: a pedal on a piano that moves the action closer to the
         strings and so soften the sound

Moby Thesaurus II by Grady Ward, 1.0:

48 Moby Thesaurus words for "soft pedal":
   allow for, baffle, choke, choke off, color, cushion, damp, dampen,
   deaden, deafen, diminish, dull, dumbfound, ease, extenuate, gag,
   gloss over, hush, hush-hush, ignore, lessen, make allowance for,
   mince, mitigate, muffle, mute, muzzle, palliate, play down,
   put to silence, quiet, quieten, shush, shut down on, silence,
   slur over, soften, squash, squelch, stifle, still, stop,
   strike dumb, subdue, throttle, tone down, varnish, whitewash