the part of a phone, musical instrument, or other device that goes near or between the lips

To play the recorder, blow gently into the mouthpiece. 演奏直笛时，要含住吹口舒缓地吹奏。

a person or a newspaper that only expresses the opinions of one particular organization

This newspaper is just a Republican mouthpiece. 这家报纸只不过是共和党的传声筒。