Not on the rocks (4)
I believe the answer is:
neat
'not on the rocks' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for neat that I've seen before include "without water being added" , "Tidy and uncluttered" , "Steers" , "Drink with no water added" , "Tidy - undiluted" .)