mouthpiece

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A part, as of a musical instrument or a telephone, that functions in or near the mouth.
2. n. Sports A protective rubber device worn over the teeth, as by boxers.
3. n. Informal One, such as a spokesperson, through which views are expressed.
4. n. Slang A defense lawyer.

Century Dictionary and Cyclopedia

1. n. In an instrument or utensil made to be inserted or applied to the mouth, the part which touches the lips or is held in the mouth, as in a musical instrument, a tobacco-pipe, cigar-holder, etc. See cut under clarinet.
2. n. One who delivers the opinions of others; one who speaks on behalf of others: as, the mouthpiece of an assembly.

Wiktionary

1. n. A part of any device that functions in or near the mouth, especially of a telephone or musical instrument
2. n. A spokesman who speaks on behalf of someone else
3. n. slang A lawyer for the defense

GNU Webster's 1913

1. n. The part of a musical or other instrument to which the mouth is applied in using it.
2. n. An appendage to an inlet or outlet opening of a pipe or vessel, to direct or facilitate the inflow or outflow of a fluid.
3. n. One who delivers the opinion of others or of another; a spokesman.
4. n. slang A person's lawyer.

WordNet 3.0

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