Sharpens (5)
I believe the answer is:
hones
'sharpens' is the definition.
(honing is a kind of sharpening)
This is all the clue.
(Other definitions for hones that I've seen before include "Sharpens on strap, say razor" , "Sharpens as on whetstone" , "gets sharp" , "Perfects, sharpens" , "Sharpens, like knife on stone" .)