Clean; fine powder (4)
I believe the answer is:
dust
This clue is a double definition.
'clean' is the first definition.
(dust can mean to clean up dust)
'fine powder' is the second definition.
(I've seen this in another clue)
(Other definitions for dust that I've seen before include "Powdery matter" , "Fine powdery material that can be blown about in the air" , "Fine dirt particles" , "The mortal remains" , "Do household cleaning" .)