Rum and water (4)
I believe the answer is:
grog
'rum and water' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for grog that I've seen before include "Old sailors' tipple" , "The old sailor's tradition drink" , "Drink of spirits mixed with water" , "Mixture of spirit and water" , "Sailors' drink of rum and water" .)