telephone receiver vs earpiece

telephone receiver and earpiece both are nouns.

Word	Noun	Adjective	Verb	Adverb
telephone receiver	Yes	No	No	No
earpiece	Yes	No	No	No

As nouns, earpiece is a hypernym of telephone receiver; that is, earpiece is a word with a broader meaning than telephone receiver:

telephone receiver: earphone that converts electrical signals into sounds
earpiece: electro-acoustic transducer for converting electric signals into sounds; it is held over or inserted into the ear

Other hypernyms of telephone receiver include earphone, headphone, phone.

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