malodor vs malodour

malodor and malodour both are nouns.

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

As nouns, malodor and malodour are synonyms defined as:

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

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