Smoothly transition (5)
I believe the answer is:
segue
'smoothly transition' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for segue that I've seen before include "Proceed immediately" , "Go on without interruption" , "Move between songs, etc, without a pause" , "Play on" , "In music, an immediate transition from one part to another" .)