A rude Wren flashed knickers? (9)
I believe the answer is:
underwear
'knickers?' is the definition.
(I've seen this before)
'a rude wren flashed' is the wordplay.
'flashed' indicates anagramming the letters (I've seen 'flash' mean this).
'a'+'rude'+'wren'='arudewren'
'arudewren' anagrammed gives 'UNDERWEAR'.
(Other definitions for underwear that I've seen before include "Garments worn next to the skin" , "Possibly slips" , "Drawers" , "Bloomers" , "Smalls,shorts,lingerie etc" .)