arousal vs necking

arousal and necking both are nouns.

Word	Noun	Adjective	Verb	Adverb
arousal	Yes	No	No	No
necking	Yes	No	No	No

As nouns, necking is a hyponym of arousal; that is, necking is a word with a more specific, narrower meaning than arousal:

arousal: mutual sexual fondling prior to sexual intercourse
necking: affectionate play (or foreplay without contact with the genital organs)

Other hyponyms of arousal include caressing, cuddling, fondling, hugging, kissing, petting, smooching, snuggling, feel.

arousal (noun)	necking (noun)
the act of arousing	affectionate play (or foreplay without contact with the genital organs)
mutual sexual fondling prior to sexual intercourse	the molding at the top of a column
awakening from sleep
a state of heightened physiological activity