Benefit from a disguise, reportedly (5)
I believe the answer is:
avail
'benefit from' is the definition.
(I've seen this before)
'a disguise reportedly' is the wordplay.
'disguise' becomes 'veil' (I've seen this before).
'reportedly' indicates a 'sounds like' (homophone) clue.
'veil' sounds like 'vail'.
'a'+'vail'='AVAIL'
(Other definitions for avail that I've seen before include "Be useful" , "Help, benefit" , "Provide help; profit" , "Make use, take advantage" , "Be of help or advantage" .)