bitterness vs ill will

bitterness and ill will both are nouns.

Word	Noun	Adjective	Verb	Adverb
bitterness	Yes	No	No	No
ill will	Yes	No	No	No

As nouns, ill will is a hypernym of bitterness; that is, ill will is a word with a broader meaning than bitterness:

Other hypernyms of bitterness include enmity, hostility.

bitterness (noun)	ill will (noun)
the property of having a harsh unpleasant taste	a hostile (very unfriendly) disposition
a rough and bitter manner	the feeling of a hostile person
the taste experience when quinine or coffee is taken into the mouth
a feeling of deep and bitter anger and ill-will