Denshi Jisho — Online Japanese dictionary

酷 こく 1: severe; harsh; stringent; rigorous; strict; unfair;
2: (Usually written using kana alone) body (esp. of food, wine, etc.); weight; substance
Common word, Na-adjective, Noun 
過酷 かこく rigour; rigor; severity; cruelty; harsh
Common word, Na-adjective, Noun 
苛酷 かこく rigour; rigor; severity; cruelty; harsh
Na-adjective, Noun 
残酷 ざんこく cruelty; harshness
Common word, Na-adjective, Noun 
冷酷 れいこく cruelty; coldheartedness; relentless; ruthless
Common word, Na-adjective, Noun 
厳酷 げんこく severity; rigor; rigour
Na-adjective, Noun 
惨酷 ざんこく atrocity; cruelty; brutality
Na-adjective, Noun 
峻酷 しゅんこく severe (personality); unaffected by love
Noun 
残忍冷酷 ざんにんれいこく atrocious and cold-blooded; cruel; brutal; merciless
Noun, Na-adjective 

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