Sandpaper coating (4)
I believe the answer is:
grit
'sandpaper coating' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for grit that I've seen before include "Indomitability" , "Bottle" , "Fortitude" , "Particles of stone/sand" , "Guts and gumption" .)