… alert after a wash (5)
I believe the answer is:
awake
'alert' is the definition.
(synonyms)
'after a wash' is the wordplay.
'after' is a charade indicator (letters next to each other).
'wash' becomes 'wake' (I've seen this before).
'a' next to 'wake' is 'AWAKE'.
(Other definitions for awake that I've seen before include "Come to" , "Completely conscious" , "Conscious, aware" , "Conscious and (usually) open-eyed" , "Not asleep" .)