foursome vs quadruplet

foursome and quadruplet both are nouns.

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

As nouns, foursome and quadruplet are synonyms defined as:

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

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

foursome (noun)	quadruplet (noun)
four people considered as a unit	a set of four similar things considered as a unit
the cardinal number that is the sum of three and one	one of four children born at the same time from the same pregnancy
	the cardinal number that is the sum of three and one