odor vs aroma

odor and aroma both are nouns.

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

As nouns, odor and aroma are synonyms defined as:

Other synonyms of odor include odour, olfactory property, scent, smell.

As nouns, aroma is a hyponym of odor; that is, aroma 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
aroma: a distinctive odor that is pleasant

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