Waistband is as he revealed (4)
I believe the answer is:
sash
'waistband' is the definition.
(I know that waistband can be written as sash)
'is as he revealed' is the wordplay.
'revealed' indicates a hidden word (I've seen 'revealing' mean this).
'SASH' can be found hidden inside 'is as he'.
(Other definitions for sash that I've seen before include "Sliding window frame" , "Girdle" , "Decorative band" , "Piece of cloth round waist or shoulder" , "Ribbon worn over the shoulder" .)