Sharp fragment (8)
I believe the answer is:
splinter
'sharp fragment' is the definition.
'splinter' can be an answer for 'fragment' (splintering is a kind of fragmenting). I also know that 'sharp' relates to this answer.
This is all the clue.
(Other definitions for splinter that I've seen before include "Break into small pieces" , "Rent slip? (anag)" , "Shard" , "Sharp piece of glass or metal - shatter" , "Long thin fragment" .)