Source : Webster's Revised Unabridged Dictionary (1913)

Sounding-board \Sound"ing-board`\, n.
   1. (Mus.) A thin board which propagates the sound in a piano,
      in a violin, and in some other musical instruments.

   2. A board or structure placed behind or over a pulpit or
      rostrum to give distinctness to a speaker's voice.

   3. pl. See {Sound boarding}, under {Sound}, a noise.