heterosexuality vs sex activity

heterosexuality and sex activity both are nouns.

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

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

heterosexuality: a sexual attraction to (or sexual relations with) persons of the opposite sex
sex activity: activities associated with sexual intercourse

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

heterosexuality (noun)	sex activity (noun)
a sexual attraction to (or sexual relations with) persons of the opposite sex	activities associated with sexual intercourse