Makes smaller (5)
I believe the answer is:
'makes smaller' is the definition.
(paring is a kind of making smaller)
This is the entire clue.
(Other definitions for pares that I've seen before include "Trims by cutting as with pencil" , "Trims, say a pencil" , "Sharpens in spare way" , "Shaves pencil to sharpen" , "Sharpens like pencil" .)