Actor ____ Baldwin (4)
I believe the answer is:
alec
'actor baldwin' 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 "Boy's name (a smart one?)" , "Guinness (a smart lad?)" , "A smart . . . . is a know-all in lace" , "Smart ..., he thinks he knows everything" , "Smart chap" .)