Dry river, save bottles (4)
I believe the answer is:
brut
'dry' is the definition.
('brut' can be similar in meaning to 'dry')
'river save bottles' is the wordplay.
'river' becomes 'r'.
'save' becomes 'but' (I've seen this before).
'bottles' means one lot of letters goes inside another ('bottle' can mean to contain).
'r' put inside 'but' is 'BRUT'.
(Other definitions for brut that I've seen before include "(Of sparkling wine) extremely dry" , "one type of champagne" , "Of champagne, not sweet" , "Dry (of champagne)" , "Unsweetened; very dry" .)