aplomb
/əˈplɒm/noun
mass noun
- self-confidence or assurance, especially when in a demanding situation（尤指在严峻的形势下）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。
词源
late 18th cent. （in the sense 'perpendicularity， steadiness'）： from French， from à plomb 'according to a plummet'.