rancor vs bitterness

rancor and bitterness both are nouns.

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

As nouns, rancor and bitterness are synonyms defined as:

Other synonyms of rancor include gall, rancour, resentment.

rancor (noun)	bitterness (noun)
a feeling of deep and bitter anger and ill-will	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