septet vs seven

septet and seven both are nouns.

Word	Noun	Adjective	Verb	Adverb
septet	Yes	No	No	No
seven	Yes	Yes	No	No

As nouns, septet and seven are synonyms defined as:

Other synonyms of septet include 7, heptad, septenary, sevener, VII.

septet (noun)	seven (noun)
a musical composition written for seven performers	one of four playing cards in a deck with seven pips on the face
seven people considered as a unit	the cardinal number that is the sum of six and one
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

septet (adjective)	seven (adjective)
	being one more than six