Ebb or wane (6)
I believe the answer is:
recede
This clue is a double definition.
'ebb' is the first definition.
(I know that ebb is a more specific form of the action recede)
'wane' is the second definition.
(thesaurus)
(Other definitions for recede that I've seen before include "Decline" , "Go backwards" , "Become more distant" , "Withdraw" , "Start balding" .)