牢 prison; jail; hardness 7 strokes. Newspaper frequency rank 2472. Readings ロウ (on reading): 堅牢 (けんろう) solid; 牢獄 (ろうごく) prison かたい (kun reading) ひとや (kun reading) Components 宀 牛 宀 radical roof 牛 radical cow Words using 牢 堅牢 (けんろう) solid 牢獄 (ろうごく) prison 牢 (ろう) prison 牢屋 (ろうや) jail 入牢 (にゅうろう) imprisonment 28 words in all. Jinuma: Japanese Dictionary · Word lists