Trims back (5)
I believe the answer is:
pares
'trims back' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for pares that I've seen before include "Trims, say a pencil" , "Sharpens like pencil" , "Trims by cutting away" , "Shaves pencil to sharpen" , "Sharpens in spare way" .)