earphone vs earpiece

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. 

earpiece

noun
  • A receiver of a telephone to hold near to one's ear. 

  • The arm on a pair of glasses that hooks over the ear to hold them in place. 

  • A speaker placed inside or held near to the ear. 

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