promiscuousness vs sex activity

promiscuousness and sex activity both are nouns.

Word	Noun	Adjective	Verb	Adverb
promiscuousness	Yes	No	No	No
sex activity	Yes	No	No	No

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

promiscuousness: indulging in promiscuous (casual and indiscriminate) sexual relations
sex activity: activities associated with sexual intercourse

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

promiscuousness (noun)	sex activity (noun)
indulging in promiscuous (casual and indiscriminate) sexual relations	activities associated with sexual intercourse