Mouth"piece` (?), n. 1. The part of a musical or other instrument to which the mouth is applied in using it; as, the mouthpiece of a bugle, or of a tobacco pipe.

2. An appendage to an inlet or outlet opening of a pipe or vessel, to direct or facilitate the inflow or outflow of a fluid.

3. One who delivers the opinion of others or of another; a spokesman; as, the mouthpiece of his party.

Egmont was imprudent enough to make himself the mouthpiece of their remonstrance.

• a part of any device that functions in or near the mouth, especially of a telephone or musical instrument
  
• a spokesman who speaks on behalf of someone else
  
• (slang) a lawyer for the defense