Nouns

(n)mouthpiecea part that goes over or into the mouth of a person“the mouthpiece of a respirator”
(n)mouthpiecean acoustic device; the part of a telephone into which a person speaks
(n)mouthpiece, moutha spokesperson (as a lawyer)
(n)mouthpiece, gumshield(especially boxing) equipment that protects an athlete's mouth
(n)mouthpiecethe tube of a pipe or cigarette holder that a smoker holds in the mouth
(n)mouthpiece, embouchurethe aperture of a wind instrument into which the player blows directly