quartet vs foursome

quartet and foursome both are nouns.

Word	Noun	Adjective	Verb	Adverb
quartet	Yes	No	No	No
foursome	Yes	No	No	No

As nouns, quartet and foursome are synonyms defined as:

Other synonyms of quartet include quartette.

As nouns, quartet and foursome are synonyms defined as:

quartet and foursome: the cardinal number that is the sum of three and one

Other synonyms of quartet include 4, four, IV, Little Joe, quadruplet, quatern, quaternary, quaternion, quaternity, tetrad.

quartet (noun)	foursome (noun)
a musical composition for four performers	four people considered as a unit
four people considered as a unit	the cardinal number that is the sum of three and one
a set of four similar things considered as a unit
four performers or singers who perform together
the cardinal number that is the sum of three and one