rancour vs rancor

rancour and rancor both are nouns.

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

As nouns, rancour and rancor are synonyms defined as:

Other synonyms of rancour include bitterness, gall, resentment.

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