Overly confident (4)
I believe the answer is:
smug
'overly confident' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for smug that I've seen before include "Prim" , "Be envious of" , "Self-satisfied, stuffy" , "Full of oneself" , "Self-righteously complacent" .)