noun (n)

• a part that goes over or into the mouth of a person(noun.artifact)

  Example:
  The mouthpiece of a respirator.
  

  source: wordnet30
• an acoustic device; the part of a telephone into which a person speaks(noun.artifact)

  source: wordnet30
• a spokesperson (as a lawyer)(noun.person)

  Synonym:
  mouth
  

  source: wordnet30
• (especially boxing) equipment that protects an athlete's mouth(noun.artifact)

  Synonym:
  gumshield
  

  source: wordnet30
• the tube of a pipe or cigarette holder that a smoker holds in the mouth(noun.artifact)

  source: wordnet30
• the aperture of a wind instrument into which the player blows directly(noun.artifact)

  Synonym:
  embouchure
  

  source: wordnet30
• 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.(noun)

  source: webster1913