Smug smile (5)
I believe the answer is:
smirk
'smug smile' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for smirk that I've seen before include "Complacent smile" , "Smug look" , "Self-satisfied smile" , "Smug smile" , "Derisive smile" .)