II vs pair

II and pair both are nouns.

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

As nouns, pair is a hyponym of II; that is, pair 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
pair: two items of the same kind

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

II (noun)	pair (noun)
the cardinal number that is the sum of one and one or a numeral representing this number	two people considered as a unit
	a set of two similar things considered as a unit
	a poker hand with 2 cards of the same value
	two items of the same kind

II (verb)	pair (verb)
	engage in sexual intercourse
	bring two objects, ideas, or people together
	arrange in pairs
	occur in pairs
	form a pair or pairs