petting vs snogging

petting and snogging both are nouns.

Word	Noun	Adjective	Verb	Adverb
petting	Yes	No	No	No
snogging	Yes	No	No	No

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

petting: affectionate play (or foreplay without contact with the genital organs)
snogging: (British informal) cuddle and kiss

petting (noun)	snogging (noun)
affectionate play (or foreplay without contact with the genital organs)	(British informal) cuddle and kiss