odor vs malodour

odor and malodour both are nouns.

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

As nouns, malodour is a hyponym of odor; that is, malodour is a word with a more specific, narrower meaning than odor:

odor: the sensation that results when olfactory receptors in the nose are stimulated by particular chemicals in gaseous form
malodour: a distinctive odor that is offensively unpleasant

Other hyponyms of odor include scent, aroma, fragrance, perfume, scent, fetor, foetor, malodor, mephitis, reek, stench, stink, acridity, stank.

odor (noun)	malodour (noun)
any property detected by the olfactory system	a distinctive odor that is offensively unpleasant
the sensation that results when olfactory receptors in the nose are stimulated by particular chemicals in gaseous form