D defs.my
Entry 4 senses Webster, 1913

Mouthpiece

/mouth'-pēsˌ/ · Mouth·piece · IPA /ˈmaʊθˌpiːs/
01 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.
  1. 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. 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. 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.” Motley.
  4. 4.
    A person's lawyer.[slang]