Draconian, Tartarean, animal, animalian, animalic, animalistic, anthropophagous, atrocious, barbaric, barbarous, beastlike, beastly, bestial, bloodthirsty, bloody, bloody-minded, brutal, brutalized, brute, brutelike, brutish, cannibalistic, cruel, cruel-hearted, demoniac, demoniacal, devilish, diabolic, dumb, fell, feral, ferocious, fiendish, fiendlike, fierce, hellish, infernal, inhuman, inhumane, instinctive, instinctual, mindless, murderous, nonrational, ruthless, sadistic, sanguinary, sanguineous, satanic, savage, sharkish, slavering, truculent, unchristian, uncivilized, unhuman, vicious, wolfish, zoic, zooidal, zoologic

For further exploring for "subhuman" in Webster Dictionary Online