Clean frock (5)
I believe the answer is:
dress
This clue is a double definition.
'clean' is the first definition.
(I've seen this before)
'frock' is the second definition.
(I know that frock can be written as dress)
(Other definitions for dress that I've seen before include "Something made from fabric" , "Costume" , "One-piece garment" , "This woman might slip on" , "Cultivate < tidy" .)