II vs twosome

II and twosome both are nouns.

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

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

II: 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 II include craps, snake eyes, brace, couple, couplet, distich, duad, duet, duo, dyad, pair, span, twain, yoke.

II (noun)	twosome (noun)
the cardinal number that is the sum of one and one or a numeral representing this number	a pair who associate with one another
	two items of the same kind