stench vs mephitis

stench and mephitis both are nouns.

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

As nouns, stench and mephitis are synonyms defined as:

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

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