Source : Webster's Revised Unabridged Dictionary (1913)

Piano \Pi*an"o\, Pianoforte \Pi*an"o*for`te\, n. [It. piano soft
   (fr. L. planus even, smooth; see {Plain}, a.) + It. forte
   strong, fr. L. fortis (see {Fort}).] (Mus.)
   A well-known musical instrument somewhat resembling the
   harpsichord, and consisting of a series of wires of graduated
   length, thickness, and tension, struck by hammers moved by
   keys.

   {Dumb piano}. See {Digitorium}.

   {Grand piano}. See under {Grand}.

   {Square piano}, one with a horizontal frame and an oblong
      case.

   {Upright piano}, one with an upright frame and vertical
      wires.

Source : WordNet®

pianoforte
     n : a stringed instrument that is played by depressing keys that
         cause hammers to strike tuned strings and produce sounds
         [syn: {piano}, {forte-piano}]