barbaric / barbarous / barbarian
Cruel or crude, savagely cruel, and the person.
Barbaric means crude or cruel, sometimes with a note of raw vigor. Barbarous is harsher: savagely cruel or uncivilized. A barbarian is the person. The words overlap. If you mean only “very cruel,” barbarous is the sharper word. If you mean “rough, unrefined,” barbaric will do.
Examples
Use a barbaric yawp
Use a barbarous punishment
Use The barbarian army crossed the river.
Avoid a barbarian punishment (If you mean the act was cruel, not that a barbarian performed it.)