Drink cold Guinness? (4)
I believe the answer is:
alec
'guinness?' is the definition.
(actor Alec Guinness)
'drink cold' is the wordplay.
'drink' becomes 'ale' (type of beer).
'cold' becomes 'c' (eg on taps).
'ale'+'c'='ALEC'
(Other definitions for alec that I've seen before include "Boy's name (a smart one?)" , "Smart man?" , "Guinness (a smart lad?)" , "Sir - Douglas-Home, former PM" , "Actor Guinness is smart" .)