earpiece vs headphone

earpiece and headphone both are nouns.

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

As nouns, earpiece and headphone are synonyms defined as:

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

Other synonyms of earpiece include earphone, phone.

earpiece (noun)	headphone (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