mouthpiece in WordNet English dictionary

1. the aperture of a wind instrument into which the player blows directly
   mouthpiece  embouchure 
   
2. (especially boxing) equipment that protects an athlete's mouth
   mouthpiece  gumshield 
   
3. a spokesperson (as a lawyer)
   mouthpiece  mouth 
   
4. the tube of a pipe or cigarette holder that a smoker holds in the mouth
   mouthpiece 
   
5. an acoustic device; the part of a telephone into which a person speaks
   mouthpiece 
   
6. a part that goes over or into the mouth of a person
   "the mouthpiece of a respirator"
   mouthpiece