roll in the hay vs coitus

roll in the hay and coitus both are nouns.

Word	Noun	Adjective	Verb	Adverb
roll in the hay	Yes	No	Yes	No
coitus	Yes	No	No	No

As nouns, coitus is a hypernym of roll in the hay; that is, coitus is a word with a broader meaning than roll in the hay:

roll in the hay: slang for sexual intercourse
coitus: sexual activity between individuals, especially the insertion of a man's penis into a woman's vagina until orgasm and ejaculation occur

roll in the hay (noun)	coitus (noun)
slang for sexual intercourse	sexual activity between individuals, especially the insertion of a man's penis into a woman's vagina until orgasm and ejaculation occur

roll in the hay (verb)	coitus (verb)
have sexual intercourse with