grudge vs bitterness

grudge and bitterness both are nouns.

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

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

Other hypernyms of grudge include gall, rancor, rancour, resentment.

grudge (noun)	bitterness (noun)
a resentment strong enough to justify retaliation	the property of having a harsh unpleasant taste
	a rough and bitter manner
	the taste experience when quinine or coffee is taken into the mouth
	a feeling of deep and bitter anger and ill-will

grudge (verb)	bitterness (verb)
accept or admit unwillingly
bear a grudge; harbor ill feelings