Sword with a three-sided blade (4)
I believe the answer is:
epee
'sword with a three-sided blade' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for epee that I've seen before include "Fencing blade" , "sharp-edged implement" , "Fencer's weapon" , "Bit of fencing" , "sports equipment" .)