2 vs duet

2 and duet both are nouns.

Word	Noun	Adjective	Verb	Adverb
2	Yes	Yes	No	No
duet	Yes	No	No	No

As nouns, duet is a hyponym of 2; that is, duet is a word with a more specific, narrower meaning than 2:

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

Other hyponyms of 2 include craps, snake eyes, brace, couple, couplet, distich, duad, duo, dyad, pair, span, twain, twosome, yoke.

2 (noun)	duet (noun)
the cardinal number that is the sum of one and one or a numeral representing this number	(ballet) a dance for two people (usually a ballerina and a danseur noble)
	a musical composition for two performers
	a pair who associate with one another
	two performers or singers who perform together
	two items of the same kind

2 (adjective)	duet (adjective)
being one more than one