sexual activity vs gender

sexual activity and gender both are nouns.

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

sexual activity (noun)	gender (noun)
activities associated with sexual intercourse	the properties that distinguish organisms on the basis of their reproductive roles
	a grammatical category in inflected languages governing the agreement between nouns and pronouns and adjectives; in some languages it is quite arbitrary but in Indo-European languages it is usually based on sex or animateness