earpiece vs earphone

earpiece and earphone both are nouns.

Word	Noun	Adjective	Verb	Adverb
earpiece	Yes	No	No	No
earphone	Yes	No	No	No

As nouns, earpiece and earphone are synonyms defined as:

earpiece and earphone: electro-acoustic transducer for converting electric signals into sounds; it is held over or inserted into the ear

Other synonyms of earpiece include headphone, phone.

earpiece (noun)	earphone (noun)
electro-acoustic transducer for converting electric signals into sounds; it is held over or inserted into the ear	electro-acoustic transducer for converting electric signals into sounds; it is held over or inserted into the ear