conjoin vs couple

conjoin is not a noun while couple is a noun.

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

As verbs, couple is a hyponym of conjoin; that is, couple is a word with a more specific, narrower meaning than conjoin:

conjoin (noun)	couple (noun)
	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

conjoin (verb)	couple (verb)
make contact or come together	engage in sexual intercourse
take in marriage; married	link together
	bring two objects, ideas, or people together
	form a pair or pairs