grievance vs bitterness

grievance and bitterness both are nouns.

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

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

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

grievance (noun)	bitterness (noun)
a complaint about a (real or imaginary) wrong that causes resentment and is grounds for action	the property of having a harsh unpleasant taste
an allegation that something imposes an illegal obligation or denies some legal right or causes injustice	a rough and bitter manner
a resentment strong enough to justify retaliation	the taste experience when quinine or coffee is taken into the mouth
	a feeling of deep and bitter anger and ill-will