Ran'cor·ous (-ŭs) adjective [ Old French 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. Found on http://www.encyclo.co.uk/webster/R/9