Abrasive powder (5)
I believe the answer is:
emery
'abrasive powder' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for emery that I've seen before include "Hard black-grey mineral used in grinding and polishing" , "Coating on paper used as an abrasive" , "Abrasive form of corundum" , "Abrasive material" , "Hard, grey-black mineral used as 11 down" .)