quartette vs opus

quartette and opus both are nouns.

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

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

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

quartette (noun)	opus (noun)
a musical composition for four performers	a musical work that has been created
four people considered as a unit
a set of four similar things considered as a unit
four performers or singers who perform together