diamond in the rough

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释义
未经雕琢之钻石 ; 深藏不漏
A person whose goodness or other positive qualities are hidden by a harsh or unremarkable surface appearance.

例句
Jane: A regular saint. See, there you go. It's obvious Watson here is a diamond in the rough. (The Mentalist)
华生：你是圣人呐。显然华生是个深藏不露的人。（超感神探）