Add ice cubes to (4)
I believe the answer is:
cool
'add ice cubes to' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for cool that I've seen before include "Moderately cold" , "Modern calmness, brrr!" , "At lowish temperature" , "Calm and unemotional" , "Neither warm nor very cold" .)