THESAURUS
unforgiving
bowelless, cruel, dog-eat-dog, flinty, hard, harsh, heartless, inclement, inexorable, merciless, pitiless, relentless, remorseless, ruthless, uncompassionate, uncompassioned, unfeeling, unmerciful, unpitiful, unpitying, unremorseful, unsympathetic, unsympathizing, unyielding, without mercy
ROGET THESAURUS
unforgiving
Revenge
N
revenge, revengement, vengeance, avengement, avengeance, sweet revenge, vendetta, death feud, blood for blood retaliation, day of reckoning, rancor, vindictiveness, implacability, malevolence, ruthlessness, avenger, vindicator, Nemesis, Eumenides, revengeful, vengeful, vindictive, rancorous, pitiless, ruthless, rigorous, avenging,
unforgiving, unrelenting, inexorable, stony-hearted, implacable, relentless, remorseless, aeternum servans sub pectore vulnus, rankling, immitigable, manet ciratrix, manet alid mente repostum, dies irae dies illa, in high vengeance there is noble scorn, inhumanum verbum est ultio, malevolus animus abditos dentes habet, now infidel I have thee on the hip.