Same word as unkind:

barbarous, brutal, cold-blooded, coldhearted, cruel, hard-hearted, harsh, hateful, heartless, inconsiderate, inhuman, inhumane, insensitive, malevolent, malicious, malignant, mean, nasty, sadistic, savage, spiteful, thoughtless, uncaring, uncharitable, unfeeling, unfriendly, unsympathetic