mouthpiece (n.) Look up mouthpiece at
also mouth-piece, 1680s, "casting fitted on an open end of a pipe, etc.," from mouth (n.) + piece (n.). Meaning "piece of a musical instrument that goes in the mouth" is from 1776. Sense of "one who speaks on behalf of others" is from 1805; in the specific sense of "lawyer" it is first found 1857.