mouthpiece

(noun) a part that goes over or into the mouth of a person. Example: "The mouthpiece of a respirator."

(noun) an acoustic device; the part of a telephone into which a person speaks.

(noun) a spokesperson (as a lawyer). Synonyms: mouth.

(noun) (especially boxing) equipment that protects an athlete's mouth. Synonyms: gumshield.

(noun) the tube of a pipe or cigarette holder that a smoker holds in the mouth.

(noun) the aperture of a wind instrument into which the player blows directly. Synonyms: embouchure.