Cold one (4)
I believe the answer is:
beer
'cold one' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for beer that I've seen before include "Hop drink" , "It may be 13 across-ed!" , "... this at pub?" , ""Give me a woman who loves __ and I will conquer the world" (Kaiser Wilhelm)" , "Ale, lager etc" .)