Definitions of piano:

• noun:   a stringed instrument that is played by depressing keys that cause hammers to strike tuned strings and produce sounds
• noun:   (music) low loudness
• adjective:   used chiefly as a direction or description in music

  Example: "The piano passages in the composition"

• adverb:   used as a direction in music; to be played relatively softly
• name:  A surname (very rare: popularity rank in the U.S.: #20615)