septet vs musical group

septet and musical group both are nouns.

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

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

Other hypernyms of septet include musical organisation, musical organization.

septet (noun)	musical group (noun)
a musical composition written for seven performers	an organization of musicians who perform together
seven people considered as a unit
a set of seven similar things considered as a unit
seven performers or singers who perform together
the cardinal number that is the sum of six and one