malodour vs mephitis

malodour and mephitis both are nouns.

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

As nouns, malodour and mephitis are synonyms defined as:

malodour and mephitis: a distinctive odor that is offensively unpleasant

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

malodour (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