Flow back, as the tide (3)
I believe the answer is:
ebb
'flow back as the tide' 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 "Abate" , "state of decline" , "Go out like tide (3)" , "Not to wax" , "(Water) recede" .)