[əˈplɒm]noun
[mass noun]self-confidence or assurance, especially when in a demanding situation
（尤指在苛刻的情形中）泰然自若，沉着，处变不惊
Diana passed the test with aplomb.
戴安娜沉着地通过了考试。

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语源
late 18th cent. (in the sense 'perpendicularity, steadiness'): from French, from à plomb 'according to a plummet'