Finished disguise, except the front (4)
I believe the answer is:
over
'finished' is the definition.
(similar in meaning)
'disguise except the front' is the wordplay.
'disguise' becomes 'cover' (I've seen this before).
'except the front' means to remove the first letter (the letter at the front is removed).
'cover' with its initial letter taken away is 'OVER'.
(Other definitions for over that I've seen before include "Finished like cricket session" , "jumped fence" , "Division of play in cricket" , "remaining" , "Given too much money" .)