two vs couple

two and couple both are nouns.

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

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

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

two (noun)	couple (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	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

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

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