Source : Webster's Revised Unabridged Dictionary (1913)

Rancorous \Ran"cor*ous\, a. [OF. rancuros.]
   Full of rancor; evincing, or caused by, rancor; deeply
   malignant; implacably spiteful or malicious; intensely
   virulent.

         So flamed his eyes with rage and rancorous ire.
                                                  --Spenser.

Source : WordNet®

rancorous
     adj : showing deep-seated resentment; "preserve...from rancourous
           envy of the rich"- Aldous Huxley