2 vs couple

2 and couple both are nouns.

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

As nouns, couple is a hyponym of 2; that is, couple 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
couple: two items of the same kind

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

2 (noun)	couple (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
	a pair of people who live together
	(physics) something joined by two equal and opposite forces that act along parallel lines
	two items of the same kind
	a small indefinite number

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

2 (verb)	couple (verb)
	engage in sexual intercourse
	link together
	bring two objects, ideas, or people together
	form a pair or pairs