pong vs mephitis

pong and mephitis both are nouns.

Word	Noun	Adjective	Verb	Adverb
pong	Yes	No	No	No
mephitis	Yes	No	No	No

As nouns, mephitis is a hypernym of pong; that is, mephitis is a word with a broader meaning than pong:

Other hypernyms of pong include fetor, foetor, malodor, malodour, reek, stench, stink.

pong (noun)	mephitis (noun)
an unpleasant smell	a distinctive odor that is offensively unpleasant
	a poisonous or foul smelling gas emitted from the earth