What is another word for "ruthless"?

Roget's Thesaurus (1911) lists these synonyms for "ruthless": anger, animus, avenge, avengeance, avengement, avenger, bear, blood, bone, breast, breathe, crow, day, death, est, feeling, feud, for, green, harbor, have, high, hip, immitigable, implacability, implacable, inexorable, infidel, keep, malevolence, malice, noble, now, pick, pickle, pitiless, pluck, rancor, rancorous, rankle.