odor vs malodor

odor and malodor both are nouns.

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

As nouns, malodor is a hyponym of odor; that is, malodor 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
malodor: a distinctive odor that is offensively unpleasant

odor (noun)	malodor (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