Pencil remnant (3)
I believe the answer is:
nub
'pencil remnant' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for nub that I've seen before include "Metal piece" , "Central point of bun" , "Gist - kernel" , "Gist (of a matter)" , "Core, pith or gist" .)