in a steady way, without stopping and starting again:
Traffic flowed smoothly.
if a planned event, piece of work etc goes smoothly, there are no problems to spoil it:
It'll take about three hours if everything goes smoothly.
Donna keeps the office running smoothly.
if you say something smoothly, you say it in a calm and confident way:
'All taken care of,' he said smoothly.
in a way that produces a smooth surface:
The jacket fit smoothly over her hips.