Reportedly bound to ebb and flow (4)
I believe the answer is:
'ebb and flow' is the definition.
'reportedly bound' is the wordplay.
'reportedly' shows a homophone (sound like).
'bound' becomes 'tied' (I've seen this before).
'tied' sounds like 'TIDE'.
'to' acts as a link.
(Other definitions for tide that I've seen before include "Current, ebb" , "Movement of seawater" , "Moon-driven sea movement" , "Sea's ebb and flow" , "turning point" .)