rancour
Concise Oxford English Dictionary © 2008 Oxford University Press:
rancour /ˈraŋkə(r)/ (US rancor)
▶noun bitterness; resentment.
– derivatives
rancorous adjective,
rancorously adverb.
rancorous adjective,
rancorously adverb.
– origin ME: via OFr. from late L. rancor ‘rankness’ (in the Vulgate ‘bitter grudge’), rel. to L. rancidus ‘stinking’.
'rancour' also found in these Oxford entries:

