Blade worn must have edges switched (6)
I believe the answer is:
dagger
'blade' is the definition.
(I've seen this in another clue)
I cannot understand how the remainder of the clue works.
(Other definitions for dagger that I've seen before include "Macbeth's weapon" , "''Is this a ... which I see before me'' (Macbeth)" , "Stabbing weapon" , "Short knife for stabbing" , "that has an incisive point" .)