Simper (5)
I believe the answer is:
smirk
'simper' is the definition.
(I know that simper can be written as smirk)
This is the entire clue.
(Other definitions for smirk that I've seen before include "Leer" , "Complacent smile" , "Show self-complacent satisfaction" , "Smug look" , "Smile scornfully" .)