malodor vs mephitis

malodor and mephitis both are nouns.

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

As nouns, malodor and mephitis are synonyms defined as:

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

malodor (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