He turned the edge of the knife.

他使刀口卷刃[变钝].

《现代英汉综合大词典》

To blunt or dull ( the edge of a cutting instrument ).

弄钝,弄卷刃 ( 切割工具的刃 )

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The edge of the knife has turned.

刀口卷刃了.

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You have turned back the edge of his sword and have not supported him in battle.

你叫他的刀剑卷刃、叫他在争战之中站立不住.

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