The use of a veil, it's said (5)
I believe the answer is:
avail
'the use' is the definition.
(I've seen this in another clue)
'a veil it's said' is the wordplay.
'it's said' indicates a 'sounds like' (homophone) clue.
'veil' is a homophone of 'vail'.
'a'+'vail'='AVAIL'
'of' acts as a link.
(Other definitions for avail that I've seen before include "Be of help or advantage" , "See 3" , "Provide help; profit" , "Be of value to" , "Help, benefit" .)