Sailor's quaff (4)
I believe the answer is:
grog
'sailor's quaff' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for grog that I've seen before include "Mixture of spirit and water" , "Spirits and water mixture" , "Drink of spirits and water liked by sailors" , "Rum mixed with water" , "Nautical drink" .)