WordNet sense 1 (a member of an uncivilized people):

barbarian

WordNet sense 2 (a cruelly rapacious person):

beast, brute, wildcat, wolf

WordNet sense 3 (marked by extreme and violent energy):

ferocious, fierce, furious

WordNet sense 4 (acting with or marked by or resulting from great force or energy or emotional intensity):

violent

WordNet sense 5 (wild and menacing):

feral, ferine

WordNet sense 6 (in a natural state; not tamed or domesticated or cultivated):

untamed, wild

WordNet sense 7 ((of persons or their actions) able or disposed to inflict pain or suffering):

barbarous, brutal, cruel, fell, roughshod, vicious

WordNet sense 8 (lacking and reflecting lack of pity or compassion):

inhumane

WordNet sense 9 (criticize harshly or violently):

crucify, pillory

WordNet sense 10 (without civilizing influences):

barbaric, uncivilized, uncivilised

WordNet sense 11 (not having a high state of culture and social development):

noncivilised, noncivilized