Actor ____ Guinness (4)
I believe the answer is:
alec
'actor guinness' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for alec that I've seen before include "Smart boy?" , "Boy's name (a smart one?)" , "A smart . . . . is a know-all in lace" , "Actor Guinness is smart" , "Sir - Douglas-Home, former PM" .)