Fencing thrust (5)
I believe the answer is:
lunge
'fencing thrust' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for lunge that I've seen before include "Sudden forward motion" , "Thrust forward as in fencing" , "Make a thrusting forward movement" , "dive" , "Sudden thrust in fencing" .)