Act dejected (4)
I believe the answer is:
mope
'act dejected' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for mope that I've seen before include "Misery guts" , "Feel dejected and apathetic" , "Become gloomy" , "Hang around being miserable" , "Sulk; mooch" .)