quintet vs opus

quintet and opus both are nouns.

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

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

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

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