octette vs piece of music

octette and piece of music both are nouns.

Word	Noun	Adjective	Verb	Adverb
octette	Yes	No	No	No
piece of music	Yes	No	No	No

As nouns, piece of music is a hypernym of octette; that is, piece of music is a word with a broader meaning than octette:

Other hypernyms of octette include composition, musical composition, opus, piece.

octette (noun)	piece of music (noun)
a musical composition written for eight performers	a musical work that has been created
eight people considered as a unit
a set of eight similar things considered as a unit
eight performers or singers who perform together