Synonyms for Inhuman (same or very similar meaning)
WordNet sense 1 (without compunction or human feeling):
cold, insensate, cold-bloodedWordNet sense 2 (lacking and reflecting lack of pity or compassion):
inhumaneWordNet sense 3 (not human; not belonging to or produced by or appropriate to human beings):
nonhumanFrom the ODE community, based on WordNetadd/edit