sestet vs piece of music

sestet and piece of music both are nouns.

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

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

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

sestet (noun)	piece of music (noun)
a musical composition written for six performers	a musical work that has been created
a rhythmic group of six lines of verse
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