sextet vs piece of music

sextet and piece of music both are nouns.

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

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

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

sextet (noun)	piece of music (noun)
a musical composition written for six performers	a musical work that has been created
six people considered as a unit
a set of six similar things considered as a unit
six performers or singers who perform together
the cardinal number that is the sum of five and one