Learner's definition of HARDNESS
[noncount]
: the quality or state of being hard硬度；坚固 -
the hardness of a diamond金刚石的硬度
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The wood's hardness makes it suitable for carving.这种木材很坚硬，适合雕刻。
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There was a hardness [=toughness] in her voice I hadn't heard before.她的说话声里有一种我过去从未听到过的强硬语气。