Circulate (4)
I believe the answer is:
flow
'circulate' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for flow that I've seen before include "Uninterrupted stream" , "Run or move like a liquid" , "Run smoothly" , "Scapa - , Orkney anchorage" , "Trickle" .)