copulate vs couple

copulate is not a noun while couple is a noun.

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

As verbs, copulate and couple are synonyms defined as:

Other synonyms of copulate include mate, pair.

copulate (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

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