aroma vs olfactory sensation

aroma and olfactory sensation both are nouns.

Word	Noun	Adjective	Verb	Adverb
aroma	Yes	No	No	No
olfactory sensation	Yes	No	No	No

As nouns, olfactory sensation is a hypernym of aroma; that is, olfactory sensation is a word with a broader meaning than aroma:

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

Other hypernyms of aroma include odor, odour, olfactory perception, smell.

aroma (noun)	olfactory sensation (noun)
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