Green card withdrawn — complaint is included (4)
I believe the answer is:
'green' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'card withdrawn complaint is included' is the wordplay.
'card' becomes 'ace' (ace is a type of playing card).
'withdrawn complaint' becomes 'n' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'is included' means one lot of letters goes inside another.
'ace' enclosing 'n' is 'ACNE'.
(Other definitions for acne that I've seen before include "Skin problem, mainly of teenagers" , "Skin affliction" , "Problem to face in" , "Face problems" , "(Inflammation causing) spots" .)