n. - 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.
n. - An appendage to an inlet or outlet opening of a pipe or vessel, to direct or facilitate the inflow or outflow of a fluid.
n. - One who delivers the opinion of others or of another; a spokesman; as, the mouthpiece of his party.