bitterness vs acerbity

bitterness and acerbity both are nouns.

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

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

Other hyponyms of bitterness include acridity, acridness.

As nouns, bitterness and acerbity are synonyms defined as:

Other synonyms of bitterness include acrimony, jaundice, tartness, thorniness.

bitterness (noun)	acerbity (noun)
the property of having a harsh unpleasant taste	a rough and bitter manner
a rough and bitter manner	a sharp sour taste
the taste experience when quinine or coffee is taken into the mouth	a sharp bitterness
a feeling of deep and bitter anger and ill-will