grievance vs rancor

grievance and rancor both are nouns.

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

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

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

grievance (noun)	rancor (noun)
a complaint about a (real or imaginary) wrong that causes resentment and is grounds for action	a feeling of deep and bitter anger and ill-will
an allegation that something imposes an illegal obligation or denies some legal right or causes injustice
a resentment strong enough to justify retaliation