quintet vs musical group

quintet and musical group both are nouns.

Word	Noun	Adjective	Verb	Adverb
quintet	Yes	No	No	No
musical group	Yes	No	No	No

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

Other hypernyms of quintet include musical organisation, musical organization.

quintet (noun)	musical group (noun)
a musical composition for five performers	an organization of musicians who perform together
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