earphone vs mouthpiece

earphone

noun
  • A transducer that converts electric signals into sound and is held near the ear, especially as part of a telephone; an earpiece or headphone. 

mouthpiece

noun
  • The part of a telephone that is held close to the mouth. 

  • The part of a wind instrument that is held in or against the mouth. 

  • A lawyer for the defense. 

  • A spokesman; one who speaks on behalf of someone else. 

How often have the words earphone and mouthpiece occurred in a corpus of books? (source: Google Ngram Viewer )