malodour vs malodor

malodour and malodor both are nouns.

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

As nouns, malodour and malodor are synonyms defined as:

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

malodour (noun)	malodor (noun)
a distinctive odor that is offensively unpleasant	a distinctive odor that is offensively unpleasant