coitus vs sexual activity

coitus and sexual activity both are nouns.

Word	Noun	Adjective	Verb	Adverb
coitus	Yes	No	No	No
sexual activity	Yes	No	No	No

As nouns, sexual activity is a hypernym of coitus; that is, sexual activity is a word with a broader meaning than coitus:

coitus: sexual activity between individuals, especially the insertion of a man's penis into a woman's vagina until orgasm and ejaculation occur
sexual activity: activities associated with sexual intercourse

Other hypernyms of coitus include sex, sex activity, sexual practice.

coitus (noun)	sexual activity (noun)
sexual activity between individuals, especially the insertion of a man's penis into a woman's vagina until orgasm and ejaculation occur	activities associated with sexual intercourse