bitterness vs acridness

bitterness and acridness both are nouns.

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

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

Other hyponyms of bitterness include acerbity, acridity.

bitterness (noun)	acridness (noun)
the property of having a harsh unpleasant taste	extreme bitterness
a rough and bitter manner	the quality of being sharply disagreeable in language or tone
the taste experience when quinine or coffee is taken into the mouth
a feeling of deep and bitter anger and ill-will