two vs twosome

two and twosome both are nouns.

Word	Noun	Adjective	Verb	Adverb
two	Yes	Yes	No	No
twosome	Yes	No	No	No

As nouns, twosome is a hyponym of two; that is, twosome is a word with a more specific, narrower meaning than two:

two: the cardinal number that is the sum of one and one or a numeral representing this number
twosome: two items of the same kind

Other hyponyms of two include craps, snake eyes, brace, couple, couplet, distich, duad, duet, duo, dyad, pair, span, twain, yoke.

two (noun)	twosome (noun)
one of the four playing cards in a deck that have two spots	a pair who associate with one another
the cardinal number that is the sum of one and one or a numeral representing this number	two items of the same kind

two (adjective)	twosome (adjective)
being one more than one