Flow's partner (3)
I believe the answer is:
ebb
'flow's partner' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ebb that I've seen before include "Receding movement, as of a tide" , "state of decline" , "Drain away; decline" , "Outward flow of the tide" , "Not to wax" .)