sourness vs acerbity

sourness and acerbity both are nouns.

Word	Noun	Adjective	Verb	Adverb
sourness	Yes	No	No	No
acerbity	Yes	No	No	No

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

Other hyponyms of sourness include tartness, vinegariness, vinegarishness.

sourness (noun)	acerbity (noun)
the property of being acidic	a rough and bitter manner
a sullen moody resentful disposition	a sharp sour taste
the taste experience when vinegar or lemon juice is taken into the mouth	a sharp bitterness