Dirk (6)
I believe the answer is:
dagger
'dirk' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for dagger that I've seen before include "Murder weapon" , "'Short, double-edged blade (6)'" , "that has an incisive point" , "''Is this a ... which I see before me'' (Macbeth)" , "A weapon; a reference mark" .)