Use a mask, did you say? (5)
I believe the answer is:
avail
'use' is the definition.
(availing is a kind of using)
'a mask did you say?' is the wordplay.
'mask' becomes 'veil' (I've seen this before).
'did you say?' shows a homophone (sound like).
'veil' sounds like 'vail'.
'a'+'vail'='AVAIL'
(Other definitions for avail that I've seen before include "Make use, take advantage" , "Help, benefit" , "Be of value to" , "Provide help; profit" , "Be of help or advantage" .)