Use a shroud, say (5)
I believe the answer is:
avail
'use' is the definition.
(availing is a kind of using)
'a shroud say' is the wordplay.
'shroud say' becomes 'vail' (I can't explain this - if you can you should believe this answer much more).
'a'+'vail'='AVAIL'
Can you help me to learn more?
(Other definitions for avail that I've seen before include "Provide help; profit" , "Be of help or advantage" , "Be of value to" , "Make use, take advantage" , "See 3" .)