A mouthpiece is the part of a musical instrument that you put in or against your mouth to play it. On a trumpet or trombone, the mouthpiece is a small cup-shaped piece of metal that you press against your lips and buzz into. On a clarinet or saxophone, it's the part you blow through, with a thin piece of wood called a reed attached. Each instrument's mouthpiece is shaped differently because each one needs to produce different sounds.

The word also describes someone who speaks on behalf of another person or group, expressing their views and opinions rather than their own. A spokesperson for the White House might be called the president's mouthpiece, delivering messages and answering questions for the president. Sometimes this usage carries a slightly negative tone, suggesting the person has no original thoughts and is just repeating what they're told to say.

In sports, a mouthpiece (or mouthguard) is a protective device athletes wear between their teeth to prevent injuries during contact sports like football, hockey, or boxing. These mouthpieces cushion blows that might otherwise chip teeth or cause jaw injuries.