sestet vs opus

sestet and opus both are nouns.

Word	Noun	Adjective	Verb	Adverb
sestet	Yes	No	No	No
opus	Yes	No	No	No

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

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

sestet (noun)	opus (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