Hoof smoother (4)
I believe the answer is:
'hoof smoother' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for rasp that I've seen before include "Make a grating noise" , "Smoother" , "Coarse file or grating sound" , "Grating noise; file" , "Grate; scrape" .)