sex vs adult

sex and adult both are nouns.

Word	Noun	Adjective	Verb	Adverb
sex	Yes	No	Yes	No
adult	Yes	Yes	No	No

sex (noun)	adult (noun)
activities associated with sexual intercourse	any mature animal
the properties that distinguish organisms on the basis of their reproductive roles	a fully developed person from maturity onward
all of the feelings resulting from the urge to gratify sexual impulses
either of the two categories (male or female) into which most organisms are divided

sex (adjective)	adult (adjective)
	(of animals) fully developed
	designed to arouse lust

sex (verb)	adult (verb)
tell the sex (of young chickens)
to evoke sexual feelings