Sharp fragment containing tungsten (6)
I believe the answer is:
shrewd
'sharp' is the definition.
('shrewd' can be a synonym of 'sharp')
'fragment containing tungsten' is the wordplay.
'fragment' becomes 'shred' (I've seen this before).
'containing' is an insertion indicator.
'tungsten' becomes 'w' (W is the chemical symbol for tungsten).
'shred' going around 'w' is 'SHREWD'.
(Other definitions for shrewd that I've seen before include "Having good judgment" , "worldly wise" , "Canny and with sound judgement" , "Fly" , "Cunning" .)