Flow swiftly (6)
I believe the answer is:
course
'flow swiftly' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for course that I've seen before include "Layer (of bricks)" , "Direction; lecture series" , "Direction taken or intended, as in race" , "Route along which something travels" , "Route of the race" .)