get it on vs couple

get it on is not a noun while couple is a noun.

Word	Noun	Adjective	Verb	Adverb
get it on	No	No	Yes	No
couple	Yes	No	Yes	No

As verbs, couple is a hypernym of get it on; that is, couple is a word with a broader meaning than get it on:

Other hypernyms of get it on include copulate, mate, pair.

get it on (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

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