sexual activity vs necking

sexual activity and necking both are nouns.

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

sexual activity (noun)	necking (noun)
activities associated with sexual intercourse	affectionate play (or foreplay without contact with the genital organs)
	the molding at the top of a column