mouthpiece

noun

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