a ‧ plomb /əˈplɒm $ əˈplɑːm/ BrE AmE noun [uncountable] formal
[ Date: 1800-1900 ; Language: French ; Origin: 'quality of being perpendicular' , from Old French a plomb 'according to the plumb line' ]
with aplomb in a confident and skilful way, especially when you have to deal with difficult problems or a difficult situation:
Ms Sharpe handled their questions with great aplomb.