Reportedly bound to changing waters (4)
I believe the answer is:
tide
'changing waters' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
'reportedly bound' is the wordplay.
'reportedly' indicates a 'sounds like' (homophone) clue.
'bound' becomes 'tied' ('tie' can be a synonym of 'bind').
'tied' sounds like 'TIDE'.
'to' is the link.
Can you help me to learn more?
(Other definitions for tide that I've seen before include "(With time) it waits for no man" , "Season; current" , "In the main, movement" , "Rising and falling of the sea" , "Periodic flow" .)